I would say the 7D can be a bit noisy, even at 100 ISO - I found there was always some 'texture' in blue skies. Also it is very intolerant of the slightest underexposure - if you try and correct this in post, shadows get very noisy.
I found the key was to a) be very careful with exposure and b) apply a little luminance noise suppression in ACR when processing the RAWs.
Of course, the very large file also means that often you will be reducing the image in size for the final version which both reduces noise and improves sharpness.
But the 7D is a bit odd - while at 100 ISO it can't produce the silky images of an original 5D, once you go above 800 ISO it begins to show its worth. Obviously shots at 3200 & 6400 will show some noise, but until the 5D3 came along, it was probably your best bet for high ISO shooting.
You also have to look at the entire package. The AF
is very good and the ergonomics were a real step forward for Canon. A real joy to use compared to the 40D or similar models.
Colin K. Work, Pixstel