I bought the Canon 10-22 mm zoom a week ago, and I figured I would
post my impressions here. I did a simple comparison test where I
photographed a distant, flat subject with lots of details
(cobblestones) with this lens and other ones for comparison.

I post the test because:
-I was not able to find any test of this lens yet
-I read ludicrous claims that this lens would be comparable to a "L
series" one, etc...

First things first, the lens is ok for its focal length, but top sharp
it isn't. If you compare its sharpness to, say, the 50mm stopped down
to 5.6, the difference is obvious. But this comparison, although it
gave me a reference point for my test procedure, is not very
meaningfull. It does not get much sharper than a 50mm stopped around
its sweet spot.

What I find most interesting is to compare this lens to the 18-55
zoom. And there I have to say that I am a bit disapointed: it is not
much sharper.

At 18, 20 and 22 mm, the two lenses give comparable results. They both
need to be stopped down to around 8.0 to give pictures worthy of a 6
Mpixels (or 8 Mpixels) sensor.

Improvement of the 10-22 over the 18-55 are:
-less chromatic aberrations ("color fringing") in the corners
-less distortion (this is one of the best point of the 10-22: for such
a lens, distortion is very small)

But this is all. The 10-22 suffers from a combination of coma and
sphericity which severely reduces contrast, making the pictures pretty
soft. At 22mm, the 17-55 can actually look a bit sharper.

Small consolation prize: the aberrations of the 10-22 respond much
better to sharpening (on the computer) than the ones of the 18-55
(sharpening brings the color fringes out). OTOH, there are special
tools to correct color fringing, so...

My conclusion:
-for best pictures, stop down to at least 8.0 (which severely reduces
the lens usefulness indoors or when shooting casually groups of
people, two of the traditional uses for wide angles...)
-for best pictures around 20mm, use the 18-55 (which is an incredible
bargain for the price)
-but we should not forget that there aren't much competition for this
lens... (no, I have not tested the Sigma 12-24)