Ed Poor wrote:

How about a simple formula, based on what percentage of a user's edits are reverted by other users? (We might tweak this by discounting reverts from a certain class of user.)

I think Ed's proposal is the germ of an idea with merit, but it needs further refinement. We don't need to reinvent the wheel here. Maybe we could look at Kuro5hin's system for ranking articles and see if it could be adapted. Other models worth considering include: Epinions.com's Web of Trust; eBay's ratings system; Slashdot.org's Meta Moderation system. Here are a couple of URLs to articles that discuss "reputation management" on the Internet:

http://www.shorewalker.com/pages/reputation_manager-1.html

http://www.smartmobs.com/archives/cat_the_evolution_of_reputation.html