AnimeCons.com has a new feature where you can make a list of all the conventions you have attended or will attend. Then you can look up a convention and see who else is going.
All these AnimeCons.com users have said they'll be at Zenkaikon:
Why aren't you on that list? Hop to it! Sign up for the AnimeCons.com Forums and then you can create your own convention log here:
(The convention log and the AnimeCons.com Forums use the same login, so you only need one account.)
After you've logged your cons, you can even get a spiffy little signature image like I've got: