Hm, I think Fermi problems are not as much in style, but certain interviewers still ask them from time to time.

I'm thinking more about just annoying puzzle problems with one right answer, that if you don't have an "aha!" moment you'd probably never get (and remember, this is in the context of a stressful interview). Stuff like the Two Glass Balls problem:

http://sites.google.com/site/mytechnicalcollection/puzzle/tw...