Hunter-
Crap, crap, http://meta.wikipedia.org/wiki/International_logo_contest was just vandalised.
If it is ok with some people, I think I should code a feature so that non-registered users are not allowed to delete anymore than 50 characters in a row. (as you just have found out, i hacked around with difflib.php in order to get some ideas for the difflib.py that i worked on, so i could do this quickly).
This won't help at all, and will only impair normal use. Anons delete substantial amounts of text all the time, perfectly legitimately, they even help in blanking vandalism. Many anons are registered users who cannot or do not want to sign in from where they are for whatever reason.
This really reminds me of Slashdot style lameness filters -- all they accomplish is alienate users. If you want to reduce vandalism, don't make it harder to cause -- make it easier to fix. That's the wiki way. With a fast difflib, it should be possible to systematically view and flag all anonymous edits for the past x hours, for example.
Regards,
Erik