An alternative could be to have a sliding window, whereby only votes in the last month or so counts - that way votes based on old revisions age out of the system. Trouble is if a page is infrequently edited then votes should last longer (since what was voted upon a while ago will probably still be similar to the current revision), and if a page is infrequently voted upon then votes should last longer too (because otherwise your sample size will so small that just the last few votes will be able to totally skew the ratings).
Those are good points. It would be neat to use diffs to calculate how much an article has changed between edits, so if you voted 3 on a stub that was entirely rewritten (nothing in the original version was contained in the current version) your vote would have a weight of 0%, and if I voted 4 on a version that was only 50% different than the current version, my vote would have a weight of 50%. This would be hard to do on a per request basis, but would be easy to do on a daily basis and store the results in an intermediate table.
Awesome, thanks.
By the way, I might have just missed it, but if I haven't you might also want to include something somewhere about which license or licenses you're releasing your extension under ;-)
I hadn't thought that far ahead! What license are Wikipedia extensions usually released with? GPL?