The AbuseFilter extension  (often called "Edit Filter" because not everything it does is related to abuse) allows users with the correct permissions (usually admins) to set up rules that trigger on specific editing actions and patterns.
For example, here is Filter #3 on the English Wikipedia. It looks for non-autoconfirmed users making edits that result in a page being reduced from more than 500 bytes to fewer than 50 bytes. In layman's terms, it looks for new users blanking pages. When such a user tries to make such an edit, they will receive an automated warning message that suggests alternatives to blanking the page. (In this case, the user is given the opportunity to go ahead and make the change after the warning, but it's possible to also prevent the edit from occurring.) The edit is then flagged in the page history as "blanking" and will also show up on watchlists as "blanking".
All of these options are fully configurable. When the AbuseFilter finds a match, it can flag the result in the filter log, trigger only on a defined rate limit, give the user a warning, prevent the action entirely, revoke autoconfirmed status for the user, and/or tag the action in histories and watchlists.
Needless to say, this is an extremely powerful tool. It accomplishes many of the tasks that, on en.wikipedia, were previously done by bots -- tasks which we here on Wikitravel must do manually. It is also, therefore, a very dangerous tool, as a poorly constructed rule might result in widespread disruption. There is also a small performance hit, proportional to the number of rules and their complexity. I estimate we would not need very many rules, so the performance hit should be minimal, especially given the relatively low volume of edits compared to English Wikipedia.
I would recommend that this feature be limited at first to a selected subset of admins on any given Wikitravel wiki, with a view toward opening it up to all admins if deemed necessary.
-- LtPowers 08:34, 19 June 2012 (EDT)