Not so much, actually. And I was just thinking the other day about whether or not I should sell mine, too. I'm not sure, but I'm leaning that direction.
When I do use it, I tend to use it full wide. And, any more, when I'm looking for something that wide, either I wind up doing a panorama or I'm reaching for the 8-15.
At the longer end...well, since my favorite lens is the TS-E 24, it wouldn't even occur to me to grab the 16-35 for something in that focal length range. And, as I type, I've got the 1.4x mounted to the TS-E 24, and I'm just waiting for the motions to die out on a mobile wood sculpture so I can take the shot. And for when I'm not doing tripod work, I've got both the 24-105 and 35L that cover the longer end.
So, the question for me really comes down to when I'd want a 16-24 (because I've got 24-35 covered much better) that I wouldn't want the fisheye and I also wouldn't be able to do a panorama of some type. And, honestly? Unless I start doing some sort of event work in tight quarters, I really just don't see that happening all that often.