Marketing guru Seth Godin is a big fan of name tags. As he notes:
a. people don't really know everyone, even if they think they do.
b. if you don't know someone's name, you are hesitant to talk to them.
c. if you don't talk to them, you never get to know them and you both lose.
d. if you are wearing a name tag, it's an invitation to start a conversation.
The thing is, though, that you have to do them right. No teeny weeny print for names, make them double-sided, and stop using lanyards that hang to attendees' belly buttons (where did that trend come from, anyway? It makes me crazy). Another suggestion he has that I thought was a good one: