Hi Caveman,
Maybe I'm not the most exacting user of any lens; but I have been very pleased with the 10-22 since I got it. You'd already know that I love using it, just by looking at this gallery! It's lightweight, and sharp enough for almost all my purposes except when absolutely wide open (when it's still OK for some things, but noticeably softer). USM and full-time manual focus are nice too. I haven't noticed any problems with flare (except occasionally if the sun's in the shot) or CA. One big nuisance is that the lens hood is very wide, and draws attention without seeming to do much that's useful. So now if using a hood I tend to carry the one from the 24-105L (also a 77mm diameter lens), and take it off for the widest shots; but these days I'm tending not to use a hood at all because I feel less conspicuous without it. I personally have no hesitation in buying EF-S as I'm pretty sure I'm not going full-frame in the foreseeable future.
That's a bit of a ramble; I'm happy to answer more specific q's ...
