Back in the day (~1989) when Minix was hot stuff I asked a friend who went to VU a question about Minix to pass on to Tanenbaum, next thing I knew I was invited to his flat next to the Amsterdamse Bos for tea and cookies. That was a very interesting afternoon.
There's always the risk that it'll turn out that you don't like your heroes when you meet them in person.
This was around 97, and the Internet was still new to me. There was access in one lab 1 hour once a week or something like that, so the fact that he replied with some pointers to few ps files about the OS was really amazing.