I found this great piece written by Claire Bower at the BMJ. It identifies 4 areas where social media can help the organisers and participants at medical (or any other) conference.
The part that struck me was:
84% of organisers use Facebook to promote their events, while 61% use Twitter and 42% use YouTube. It seems that social media not only facilitates knowledge sharing and networking amongst attendees, it can also help create a real buzz that starts before the event and continues long after it ends.
Here's a graphic taken from the blog (credits at the bottom).