I had the pleasure of meeting Dennis Zimmer at VMworld Europe (thanks for the introduction Roland ;-), author of several books and the guy behind the biggest virtualisation site in Germany (no English translation for the site yet, but he assures me it's coming - several of his books are in English however so don't be afraid to pick them up from Amazon).
I also finally got to meet Mike Laverick in person (identified him by voice when he asked a question during the Site Recovery Manager deep dive session :-D) and met some other cool people too, as well as have a dinner with a few product managers at VMware which was great. I think easily the biggest benefit from conferences are these kinds of opportunities, and encourage anyone to make the most of any time outside of the sessions by talking to a product manager or even a complete stranger!