Hi there,
Drupal has a distributed authentication system (http://drupal.org/node/312) that allows any holder of an account from a participating site to log into another participating site using his original login (preventing namespace collision via user@sitename for the other sites).
Given the vast number of Wikipedia account holders, might not this system be useful to MediaWiki sites? Adding in some PKI to prevent "remote.spammers.biz" from entering the network (requiring participating sites to "register" with a "auth.mediawiki.org") and ideally making this protocol in concert with, and thus compatible with Drupal (why not after all; the creation of a standard cross-server authentication mechanism would be nice, no?), the smaller sites could benefit from the speed bump to vandals that registration implies without actually deterring potential contributors.
Any thoughts? -RS