Why haven't signup confirmation emails died yet?
m0digital: Good question. I'm kinda torn both ways. One advantage is that you know that the email they provided is valid so that if you do need to send them important updates it will work, otherwise there's no way to invite the users back if they haven't checked your site out in a while. There are compromises you can make like giving access to 70% of your site w/o email confirmation and the other 30% after email confirmation.  I'm not a usability expert so someone else may have a better answer.