[Mediawiki-l] Clean up users?

[Anthony Lieuallen]

SELECT 'all', count(0) FROM user
UNION
SELECT '0 edit', count(0) FROM user WHERE user_editcount = 0;

all 	count(0)
all 	22749
0 edit 	22288

All but ~500 out of ~22,000 users on my wiki have never made a single 
edit.  Is there a good way to clean out these junk records?  Is there an 
extension that puts e.g. a captcha on the user register page (not just 
edit)?