http://wiki.lesswrong.com/ is now live, for all our Wiki needs. The previous Wikia wiki has been imported. Knock yourself out on linking there from comments or blog posts (yes, you will have to link manually, there is no CamelCase convention yet on the blog and comments).
See here for proposed wiki usage guidelines - note that these do not yet seem to appear in the Wiki itself, hint hint.
I wouldn't want to substitute the best LW posts and comments for equally time consuming wiki contributions. But many of us are incapable of writing the best posts and comments, but I would guess, could do a decent job of making wiki contributions.
And like SoullessAutomaton said:
One other hueristic I was using - commenting on LW is more fun because it is social, and yeah, the karma helps too. In this context I think this is (weak) evidence that the wiki will be more subject to a collective action problem. Then again, Wikipedia exists.