As a wiki owner myself, its an issue that has to be addressed, It probably wasn't a person defacing your forum, that a script that google wikis, spiders them, and shoves the ads on, without the machine owners knowledge. (A backdoor and a simple perl script / exe could do this). Our solution was to 'protect' all important pages, which wouldn't be changed in a while. Other than that, we can only hope (With regards to 'Require registration', its not hard to register, login and use cookies to gain access to the pages :/)
With regards to the poll, i'm gonna have to go against the general population and vote YES. Its one thing to deface a wiki, its another to give a website a bad name because of it
