I've been using mailinator.com for years - they have an almost identical service (they don't allow you to send mail, though)

Another helpful use case: Some annoying sites ask you to create an account before you can browse them, but there's a faster way: Click on a 'lost password' link, and enter <website name>@mailinator.com as your email - chances are, someone else has already used mailinator to create an account, and you can re-use theirs :-)