I think there are two choices for tailors in Chicago; I had read about Boguslaw in the past, but several people have recommended Chris Despos, who posts on either this forum or askandy I believe.
here's a discussion of this very topic:http://www.styleforum.net/showthread.php?t=16217
[I actually posted this orginal topic, but when I was on vacation in the states a few weeks ago, I was closer to Atlanta. I took all of my suits and jackets to be altered to my favorite tailor, Custom Clothing of Atlanta on Barfield Road]
I believe forum member Soph has all his suits altered by Chris Despos, as far as I know-- you'll see it mentioned on the 'what are you wearing' thread here and there, and of course he seems very pleased with the results.