Lots of signups, lots of bouncing mail.
I'm afraid, registering won't reveal any link if thats why people are registering
If not, the email has to be 'valid' in so far that it exists and you can get access to it. I wouldn't recommend using an isp mail, but if your using hotmail, make sure the account is activated, since they close accounts not used in a month or so.
I would recommend yahoo.com/domain for spam addresses, signups, etc. They are stable, fast and easy to use.
Just getting a lot of mail bounces and thought it was worth posting.