You can use MeetOnCruise.com to find out who's on your cruise before you set sail.
What's hot: A social network for cruising? Why not? Just enter the name of your ship and your departure date, and you can see who else will be on board (or check "Recent cruises' to see what cruisers are talking about). It's new, so it might take a few cruises before word of it spreads. If you don't see your cruise listed, add it. The Meet On Cruise Blog is a good place to chat with people about cruising before you commit.