Some web sites require an e-mail address and send a confirming e-mail message to activate an account. The “confirmation” might be an excuse to get an e-mail address that can become a spam target.
It’s worth noting another useful site, BugMeNot.com, a huge collection of login names and passwords for sites with content behind a free “registration” requirement.
The Slashdot community reacted to the story about Ten Minute Mail by comparing it to their favorite services for temporary e-mail addresses and other anonymity tools. There’s a lot of them – no surprise in these paranoid times.