Recently, I have noticed that the "Recent Wiki Edits" box (equivalently, this page) in the sidebar seems to be almost exclusively filled with the edits from spam bots and either Gwern or Vladimir Nesov cleaning up after them (thanks!). This seems like it should be fixed, if only to save those two the time they spend on maintenance.
The wiki registration form does have a reCAPTCHA in an attempt to block spam-bots, but this is apparently not effective enough (maybe because reCAPTCHA has been cracked, or the spammers are using humans in some way).
I have some possible solutions, but I shall wait a bit before suggesting them.
(I vaguely remember there being a discussion like this previously, but I can't find it again, if it exists.)