I own a DX Sigma 10-20mm, which I used quite a bit when it was new, but find myself using less and less often when I do shoot with a DX body. I have a Nikon 20-35mm which I use occasionally, though almost as often, I shoot at 35mm on my 35-70mm. Most of the time if I want wider, I'll simply stitch multiple images together. I've got a 24mm prime somewhere too, but I'm not a big fan and frankly the 20-35mm is roughly the same quality, so I don't see the point of carrying the 24mm around. The 10-20mm is likely to start joining the 24mm on shelf duty.
For me, ultra-wides simply don't provide a field of view I find compelling most of the time. I find them useful for architecture where you can't back up due to traffic, fences, trees and the like, but seldom am I anywhere that I find the large expanse of sky good, or that I'm able to frame with a large expanse of foreground in a way that works with an ultra-wide.
Paul