I have a modest setup of 450D, Tamron 28-75 2.8 and Sigma 70-300.
Previously I've owned a Canon 10-22, 28-135 IS and 17-40L and have enjoyed each. I hate lens swapping and the weight of taking everything on holidays though and eventually sold the three, settling on the Tamron 28-75 as my walkaround lens.
Much as a I do adore the IQ of the Tamron, it's range is pretty restictive as a walkaround and I have been reading some generally very positive things about the 15-85IS, the photos in the lens thread are pretty darn good to. Although I didn't use the 10-22 much it did take some truly lovely shots and a real wide angle is what I'm missing most.
Obvious question then, how good is the 15-85 at the extreme WA and how comparable is it to the other lenses I've owned? I would be after better IQ than the 28-135 (which itself wasn't a bad lens) and ideally the 15-85 would be comparable to the Tamron which is probably a bit of an ask.
One thread I saw had a favorable comparison to the 24-105L which I always imagined to be the lens I wanted to go to next, so if it's comparable to that I'd be more than happy. I shoot mainly anything, from the grandkids (and portraits may be an upcoming big area) to flowers to architecture to art etc etc etc so I really do need a lens that will basically just live on the camera. For what I shoot, giving up the 2.8 is not a big deal, the range is what I need most although I believe there will be a fair weight gain in the Canon, but that's just something I'll have to put up with,