I have been banning a lot of IP's and domains but I recently added a domain that was used for legitimate posters a long time ago, @yahoo.co.uk. However, I have seen nothing but spam registrations using that email up to several per day. So I banned that domain. It should not effect any current users registered with emails for that domain, if you are having problems logging in and you have this domain contact me via email. No one should try to change their emails to this domain because it may ban you, then again it may not but it's probably better not to push your luck.
Wildcard banned usernames with two or more consecutive periods in them.