I may have a solution to the problems about cheaters signing up multiple e-mails. Why not have a program where you can banned the cheaters's e-mail addresses? Maybe banning certain words that the cheaters used in front of all their e-mail addresses. That way you don't banned ip numbers. Yahoo have a script programed in their groups that you can banned e-mail addresses. But I think this might be a solution as well.

useless

I think they use a random names for them. So I won't be possible to ban a certain word, and even if you do, you might be banning someone who is not a cheater!!