Another excellent question. Can you believe that you're the first person to ask me that in the seven years that I've been doing this?! I was worried about using a fisheye at first since we sat down and made a daunting list of all the shots that we needed and I was relatively new to using that lens. Guess what though! A great advantage to using a single focal length lens is that one starts seeing how to frame-up a subject on sight. When composition seemed impossible, it forced me to walk around and find angles that I'd never seen in photos before. I even started seeing fisheye images while I was dreaming, which kind of freaked me out.
Then we went to India, armed with another long list of photos to make, a guide educated at UC Berkley, and a driver that would take us off-the-beaten-path and show us things that were quirky and cool. A funny thing happened the very first day and kept happening: People actually called me over to make a portrait of them.
At first, I was taken aback by this as I hadn't planned on such photos and my mind was screaming, "Portrait with a fisheye?" I explained to our guide, and he said, "Dude, just go bang off a few frames, this guy never asks for such a thing, and he's a friend of mine." I did it, and this situation repeated itself almost every place we went. When I returned home and looked at the collection of portraits, I realized that they were some of the best work that I had ever done. You can see them here (as long as the site says active) if you're so inclined: https://plus.google.com/u/0/collection/s7zCkB