DCCWikipedia Authentication – DCCwiki
This looks like a useful solution for shared (single) sign-on between Drupal and MediaWiki, I picked it up from this thread in the drupal.org support forum. It comes with a number of warnings, but it sounds like people has tried it with great success.
I have to try it, or at least investigate how it’s build, since having both Drupal and MediaWiki installed is becoming a very common configuration for me.