I've been reading for a while (mainly to keep up with what might happen in the near future), but I felt inclined to make some comments on noise with the 7D. The first comment, is that even at ISO3200, the level of noise is much less than the grain that would have been seen on old ASA 400 film. It is also much easier to deal with than previous Canon cameras (such as the 40D), as you don't get the banding and it is much more even. That said, I tend not to go higher than ISO 1600. If I need to go higher (or if I don't need the frame rate), then I switch to the 5d MkII. However, noise is variable. Some scenes, ISO 1600 is perfectly fine, while in others it results in disturbing levels of noise. Essentially, it depends on how many shadow areas there are and whether those shadow areas are part of the subject. If you have a textured OOF background, then it tends to hide the noise somewhat too, without losing much of the fine detail, while a smooth background will make it more evident. In fact, it was only after using the 7D for some time, that I realised that part of the problem is the resolution, almost as if it is finding some sort of texture that wouldn't have been seen with lower resolution cameras. Often, the out of focus areas have a speckled appearance that isn't like noise seen in other cameras I've used, probably because it is more luminance noise than chroma, which is easily removed with a low setting in Lightroom 3.
The biggest disadvantage I have found with the 7D, is softening at narrow apertures, due to the diffraction limited affects, resulting from the small pixel size. In fact, that was the reason I ended up getting the 5D MkII for my landscape work. Of course, then I ended up using that camera for macros too, as I found it easier to focus manually, plus the images were clearner overall.
As for the 17-40. Yes, it does distort a lot, but that isn't necessarily a bad thing. Many wide-angle zooms (which is what is was designed as after all, even if it isn't that much of a wide-angle on a crop body) suffer to a greater or lesser degree from this. The trick is to make creative use of that distortion and pick and choose what subjects you use it for and how you angle the camera. If you keep the sensor parallel to the subject, then the distortion is less noticeable for many subjects and is also more easily corrected in post. The distortion is really handy for accentuating converging verticals with tall symmetrical buildings and for giving the appearance of curvature of the earth in certain landscapes and seascapes. It's not everyone's cup of tea, but it does give you something different to what everyone else is doing.
Essentially, photography is always a compromise, whatever tools you use, you simply have to explore the weaknesses and strengths of each piece of equipment and work around them. For example, as Neuroanatamist has said, the 5D is weak at focus tracking, but good at focusing in low light and producing low noise (relative to virtually any camera except the D3s and possibly the original D3). For that reason, I usually use the 7D for wildlife, but when I was photographing roding woodcocks after sunset, I used the 5D in single shot mode for optimal focusing and as low noise as possible (at least for the equipment available to me). Working around the limitations (and spending more nights attempting it), I was able to get similar quality shots to a pro wildlife photographer on his D3s, I just had to apply a bit more noise reduction at ISO3200 than he would have needed.
