I always assume if I'm going to type an e-mail address in, someone may check it. There is a fear of spam, but no one's ever been spammed by Mudcat. Folks have to type a valid e-mail into places like PalTalk to join (and I HAVE been spammed by them). I'd guess other message boards require it, but I have no firsthand knowledge.

One note - I was wrong that this is an alternative to Justa Picker's IP number idea. The IP numbers will show up regardless of whether someone is a member. The e-mail confirmation will only prevent some of the abuse of membership.