The first thing you notice is that this is not a small lightweight camera, but is a solid well built camera designed for serious use, yet despite it's size and weight it is still easy to hold and is comfortable to use, for those of you that have used the EOS 40D it has the same body shell as that, and has the advantage of using the same accessories as the EOS 40D as well.
The menu's are well laid out and easy to use making this camera easy to set up and use, the large LCD screen is bright and clear, and much higher resolution than previous EOS cameras,(920,000 pixels) excellent for manual focusing in live view and checking the focus of pictures you have already taken.

Auto focus is lightning quick and accurate under normal conditions, and even in low light conditions it is still quick. (tested with canon lenses)
Cramming 15 megapixels resolution onto a small sensor causes problems with digital noise on many cameras, but not here, digital noise (graininess) is not apparent at all until you get into the highest ISO settings (ISO-100 to 3200 is available) and even then it is well controlled, (there is also the option of setting a very high ISO-6400 or ISO-12800 setting but noise is apparent at such high settings and is best used in emergency only,) with it's 15mp resolution, even severely cropped or greatly enlarged pictures are crystal clear, (see example pictures below for details) colours are rendered accurately, even in difficult lighting conditions, when set to auto white balance, snow comes out as white snow, not bluish as on some other cameras that I have used, picture quality really is superb, and has to be seen to be believed.

One thing I have noticed, is that this camera, when it is set to program mode, has a tendancy to slightly over expose pictures under certain lighting conditions, especially Where if there is water or any other reflective surfaces present, I usually set. the camera to auto-exposure bracketing by either a 1/3 or a 2/3 of a stop to compensate for this when taking these pictures, but as it is usually less than 1 stop over exposed it is fairly easy to fix this in post processing, this is where RAW files (digital negatives) come in useful as they contain more picture information than jpegs, so over and under exposed areas can be fixed a lot easier, the camera comes supplied with very good RAW editing software, but I normally use photoshop to edit my RAW files as that is the software I am more used to using for this, you get the best of both worlds with this camera as you can record both jpeg + RAW files simultaneously. (RAW files are the raw data that a camera records and must be converted after processing to a useable picture format, such as jpeg, bmp, gif, tiff etc. that can be displayed on a PC or Mac screen, and used for printing.)
Example of picture quality even when severely cropped and enlarged

Picture 1
The clover picture above was cropped from a small portion of the full image, (approx. 10% of the original).
Picture 2
The river picture is a full uncropped frame (reduced in size to 1500 pixels wide to fall within Ciao's picture and file size guidelines), It was deliberately taken in adverse lighting conditions (just before sunset) to show up any faults such as High ISO noise

Picture 3
Is a small area of picture 2 cropped down to the railings. this area was deliberatey chosen as it is a darker & lower contrast area which will show up more noise in the picture than would a bright & high contrast area.

Notice the lack of any appreciable noise and pixellation. even at this level of cropping, fine detail is still rendered accurately (click on images 1 & 3 then select XXL view to see the fine detail of cropped images) no post processing other than cropping and resizing was applied. (more pictures will be added in due course)
Other feartures

The built in flash is adequate for most situations but if you take a lot of flash photos and need a higher output flash, then one of canon's speedlight flashes can be used instead.
It is compatible with all Canon's EX series speelight flashguns.

It has a fast 6.3 frames per second high speed continuous shooting mode,
and a 3 frames per second low speed continuous shooting mode.
It is compatible with the latest high speed, high capacity CF cards, making it possible to fit thoudands of pictures onto one card, even when shooting jpeg + RAW simultaneously at maximum resolution. I have a 32gb 133x CF card in mine and I can fit a whole days shooting onto it, and still have plenty of room to spare.

It is compatible with all canon EF and EFS lenses, and with canon's image stabilised lenses you get pin sharp pictures even in low light or with longer telephoto lenses. * (see notes below about chosing lenses for this camera.)
PRO's
Good all round performance.
Excellent picture quality.
High resolution with low noise.
Good low light performance.
Quick and accurate focusing and a very effective image stabilisation (with Canon's IS lenses)
Live view function.
6.3 frames per second continuous shooting.
Well built and strong with its metal body shell.
Takes the same accessories as the EOS 40D
Compatible with the latest high capacity CF cards.
Raw or Jpeg files are recorded, Raw+Jpeg simultaneous recording is also possible.

CON's
large and heavy.
No movie function.
No CF card supplied, so if you don't already have one, you will need to buy one before you can use it (with 15mp resolution the higher the capacity of the card the better).

In conclusion
This is an excellent camera for the serious photographer and is a worthwhile upgrade from an older camera.
If you already own an EOS 40D then the difference in performance would not warrant the expense of an upgrade, but if you want a second body with higher resolution then this would be an ideal companion to your existing EOS 40D, as most of the functions are the same and you can use all your current accessories with it.
It would also be a good back up camera for a professional photographer, who does not want to go to the expense of a second full frame pro camera.

It is more expensive than some other "prosumer" cameras, but with the features and performance that you get, it is worth every penny.
Highly recommended.
Specifications

(from the manual)

15.1 Megapixel APS-C sized CMOS Sensor
6.3fps continuous shooting, max. burst of 90 JPEGs with UDMA card
DIGIC 4 processor
ISO 100-3200, expandable to 6400 &12800
9-point wide area auto focus
3.0” Clear View VGA LCD (920,000 pixels) with Live View mode & Face Detection Live AF
Magnesium alloy body, with environmental protection
EOS Integrated Sensor Cleaning System
HDMI connection for high quality viewing and playback on a High Definition TV
Full compatibility with Canon EF and EF-S lenses and EX-series Speedlites
File formats
• RAW (.CR2; 14-bit)
• JPEG (EXIF 2.21) - Fine / Normal
• RAW + JPEG (separate files simutaneous recording)
• sRAW1 (7.1 MP)
• sRAW2 (3.8 MP)

Shooting modes
• Auto
• Creative auto
• Program AE (P)
• Shutter priority AE (Tv)
• Aperture priority AE (Av)
• Manual (M)
• Auto depth-of-field
• Portrait
• Landscape
• Close-up
• Sports
• Night portrait
• Flash off
• Camera user settings 1
• Camera user settings 2

* Notes and advice on choosing lenses for this camera.

There is often confusion for people when buying lenses for DSLR cameras (especially if they are new to DSLR's), as the actual focal length of a lens is not the same as the effective focal length that they will get on their camera, and most good camera shops have conversion charts to make this easier when advising their customers of the best lens to buy for their needs, but most online shops do not, hence the advice below.
Here's why

When you buy a lens it has a stated (actual) focal length, or range of focal lengths in the case of zoom lenses, (magnification) measured in millimeters, e.g. 100mm focal length.
The stated focal length on any lens is rated for 35mm film cameras and professional full frame DSLR cameras with a censor size of 35mm x 24mm, this is the standard rating for all SLR lenses.

The censor on this camera (and on most EOS DSLR cameras) is the "APS-C" sized censor with a measurement of 22.3mm x 14.9mm, this means that the effective focal length of the lens will be different to the stated (actual) focal length of any lens you buy when used with these cameras, this effective focal length is known as the "35mm equivalent."
This is not a fault, but is a feature of all DSLR cameras, with the exception of professional full frame cameras.

To find the 35mm equivalent of any lens used, you must multiply the stated focal length of the lens, by a factor of 1.6, thus a 100mm lens will have an effective focal length of 160mm (35mm equivalent) when used with these cameras.
This is great news if you want to use telephoto lenses for wildlife etc. as you will get higher magnification from your lens, for less cost than on a full frame camera, so a 70 - 300mm zoom lens will have a 35mm equivalent of a 112 - 480mm zoom lens.

But on the other end of the scale, wide angle lenses will be less wide, and you will need to buy a more expensive wider angle lens to compensate for the difference in focal length, thus a 10 - 22mm ultra-wide angle zoom will become a very useful 16 - 35.2mm wide angle zoom.
The standard lens on a 35mm camera is 50mm which gives approx x1 magnification, but on these cameras, it is the equivalent of an 80mm portrait lens, 31.25mm would give you the equivalent of a 50mm lens (35mm equivalent) on these cameras.

The coversion factor for Canon cameras is x1.6 of the stated focal length, other camera manufacturers may vary, so it is best to check the manual of your camera first.
So if you are new to DSLR cameras, or are upgrading from a 35mm film camera, I hope this info will help you to make the right choice when buying extra lenses for your DSLR camera, because the difference between the actual and effective focal length of a lens can significantly change the type of photo which you can use it for.