I just got my 40D today. Lucky enough to be the 1st in line to hold one at my nearest retail camera store. They were dropping from the shelves like flies just shortly after shipment. Here are my first looks.
A new design to get used to. The menu being more 1D-like the most you will have to orient yourself to is the redesigned custom functions. For example gone is the AE/AF lock mode option (one of my favorites). It is replaced with the AF-on button option. So if you are graduating from an earlier camera, get ready for some changes.
The speed is decent. 6.5 fps does give you better hit chances in areas like sports. It is only two shots shy of the 1D spec in this category just a year ago. Shutter is suprisingly much quieter. I would say almost as quiet as the venerable 10D. The viewfinder is very improved. Good to the point where the live LCD function is absolutely uneccessary. The pop-up flash sounds different.
Even though it is more "professional" than ever, it still has the consumer characteristics. This includes the basic zone and lack of soft touch shutter. But it will still satisfy proffesionals just like its predecessors.
At the price of $1299, this is a great buy in its own right. I think it is overal superior to the Nikon D200 which is now $200 more.
I am aware of the 1D Mark III's focusing issues. So far I did not detect any in this camera, but I have yet to fully deploy it on a serious assignment. I am keeping my fingers crossed.
IMHO DIGIC III does not improve image quality over DIGIC II. I may believe the the battery effiecency improvement, but I played with the Canon 1D Mark III on images from my 20Ds and 5D and found little if any difference.
Overall this is a great camera that I reccomend. It will have the widest audience out of all the cameras in Canon's EOS system. An experienced photographer with good lenses will get fine results akin to cameras like the Canon 1D family or Nikon D2 family. While beggingers may have some trouble with a camera like this, Canon has preserved the automatic modes to fall back on. But I want to stress to all that your pictures will not improve if you do not dare to explore.
My two cents