Wearing another hat I am involved in a number of Open Source Software projects. One of them had so many automated sign-up-then-spam (also known as "drive by edits") on the wiki that we had to lock the thing down and restrict who could edit and administer it.
That action sort of defeats the object of a wiki in the first place, but the devious people behind this stuff put content in which is then pulled in and included in botnet spam runs - it means they can command the bots under their control to pull in content and send it, rather than having to feed them by hand. We didn't like that, so took the only option we had available to us.
On the plus side, it has meant that we also no longer get edits made by new members which are fundamentally flawed, so we can all sit a bit easier at night
