"Do you have any questions for me?" is usually asked by the potential employer in order to politely signal the end the interview and not because he's interested in your questions.
I don't have data on "usually" but I always find it a good way to determine whether the candidate is: (1) prepared; (2) interested; and (3) thoughtful.
I have a friend who failed an interview (there was only one puzzle question and he couldn't answer it). He got the job because he asked lots of questions at the end that really showed he was interested in the position and that he was in fact smart. In the end he turned their opinions around and got a job offer.
Every single interview I've had has had about 10-20% of the time for questions baked into the schedule. I've known people who didn't get a job because they didn't ask any questions in the interview.