Wikis have been thoroughly mainstreamed now. You know how I can tell? Spammers are targeting them.
Any wiki without access control is going to get steamrolled by a bunch of Russian computers that are editing wiki pages. They replace all the legitimate content with links to porn sites, warez, viagra, get rich now, and the usual panoply of digital plaque.
The purpose does not appear to be driving traffic directly to those sites from the wikis. Instead, they are trying to pollute Google's page rankings by creating thousands upon thousands of additional inbound links.
If you run a wiki, be sure to enable access control and versioning (so you can recover after an attack). It is a shame that the open, freewheeling environment of the wiki has to end. It seems that the only way to preserve the value of the community is to weaken the core value of open participation that made the community worthwhile.