There is no max to the number of accounts that a person can have. However you can only have one per email address.
This is false. I have all of my accounts registered with the same email address.
Quote Originally Posted by 'jimbobobb',index.php?page=Thread&postID=156064#po st156064
If you create many trial accounts from the same (static) IP address, the automatic system can think that you are a spammer
This is kind of true. I don't know about the reasoning behind it, but if you try to create more than the allowed number of accounts from one ip address, you'll get that 'zomg error contact blizz' message. Exact same thing happened to me and I was able to call them to get it straightened out. Connecting to a different internet source will work as well-- my friend came over and wanted to create a trial account but it wouldn't let him on our connection. He was able to create an account by connecting to a neighbor's wireless internet.