Goo Gle is going to finally help in the Spam Wars via a No Follow tag attribute which blog software developers can use in their Comment forms to reduce the Page Rank benefit of Comment Spam. See [z2004-02-08-Comment Spam Idea] for similar idea. Here's Goo Gle's official announcement plus some comments from Dave Winer.
How might you apply this to Wiki Spam?
One idea:
follow ZWiki model of distinguishing Appends from Edits
- allow anonymous users only to Append (you could still support authentication and give out accounts with Edit privileges to some number of people).
wrap something around each Append comment's Smart Ascii as its added
when rendering a page, take any external links within such tags and add the No Follow attribute
Variant that doesn't even use No Follow tag:
limit users to Append, and remove 'http://' from the Smart Ascii itself. That way the link doesn't render.
probably have to separately handle 'href' tags in Appends - removing the 'http://' will leave an href that the browser will think is local to your server, so you'll still get a link, but it won't be valid.