There is most certainly a lot of fun to be had with fish-eye lenses, especially when used to put the observer right into the middle of whatever is happening, something at which both ultra wide-angle lenses as well as fish-eyes excel.

The thing I particularly like about fish-eyes is that they can give a nice rounded-off feeling to the composition, drawing the corners of the image slightly in, like in the following example, which would have been less effective with a normal wide-angle lense.

This image was captured on a Nikon D70s with the Nikon 10.5mm f2.8 DX fish-eye lense in the pedestrian zone of Memmingen, Germany.