This policy has been in effect for a while but never officially typed up. Basically, user accounts used for spamming will be deleted, and any account that has never been accessed after six months will be deleted.

1. The name is gibberish. Names like "XIjanawWeF" may be deleted at any time.
2. The name references adult content. The assumption here is that the account is being created to comment-spam for porn sites, and therefore is subject to immediate deletion.
3. Any account used for comment-spamming will be immediately deleted.
4. The account has not been used for over six months and has never been accessed.

Note that, as always, the ultimate rule ("anything the admins do is allowed by the rules") is in effect. If your account is deleted and you don't think it should have been, you may use the Contact form to request your account be recreated.