I like ultra-wide perspectives, but the fisheye tends to elude me. Some of my friends have had wild successes with their respective fisheye lenses, though, so I know it's just me.
That said, the Pentax 10-17 does its job. I just used it today, in fact, for my self-portrait of the day:
My other shots taken with it are here:
Flickr: aravis121's stuff tagged with fisheye
I really look forward to seeing what you do with the fisheye you decide on; it seems to be a very challenging but very rewarding type of photography.