I've deleted about 2,000 meta keys from deleted accounts (mostly spam accounts), which should make the forums run at least a little faster.
I've also deleted meta keys that were left over from the forum's split from my blog.
There is a lot more spam prevention going on now, so the spammers shouldn't even be able to register. To name a few, bb-NoSpamUser, Project Honey Pot for bbPress, Akismet, and a bot trap that I can't link to for a few reasons.
Private Messaging emails can now be disabled if you go to the forums every day. Look in your profile settings for a checkbox.