Duck.. Always wanted one after seeing that Joey and Chandler had one in their apartment (in friends). Thought it was cool, and still think it would be cool.
However, my cousin had one in her apartment and it would poop everywhere and she used to put it in the bathtub so it could swim around a bit but he flapped around and got everything wet. She set it free at a lake around here after maybe 1 week.
Nevertheless, i want one.