I use Lisp, and I research AI. I think I remember someone explaining why it's such a good language for such purposes in that in AI research, you often don't know exactly what you're trying to solve, and it is the most flexible in the range of problems you can solve. Personally, I was sold when someone remarked that Lisp users will tell you it's the most powerful language in existence, and people using other languages don't, so there must be something to that.