Well, it has started to happen on a more regular basis I think, just as I was starting to get comfortable with wikis. Many of the Ruby folks are noticing an increase in wiki spam, which I guess is mostly done in some attempt to increase page ranking I'm told.
I guess we'll have to all put captcha's in our wikis in the future. Death to the wiki spammers.
Read-mostly Wikis (Score:2)
The Wiki for the AYE Conference [ayeconference.com] is publicly readable. Write access requires a password, which we give out to current and past attendees. This model has worked quite well for us for the last four years.