As of now are all outbound links from the english Wikipedia Site using the NOFOLLOW attribute, no exceptions.
No matter where you place it, Article Page, Talk Page, User Page, Project Page, whatever. No Link will get any credit at the major search engines.
This will not eliminate SPAM at Wikipedia, but it will over time certainly reduce it a bit. Especially the spam of invisible pages that have virtually no traffic but at least some PageRank is now virtually a waste of time for any spammer.
Spamming of areas with traffic was futile already without the NOFOLLOW attribute in place, since Editors remove the SPAM within hours or even minutes after it happened.
Update 1: Wikipedia Mailing List Message about the official decision by Jimbo Wales (Wikipedia Co-Founder)Â
Update 2: ThereÂ seems to be some need to explain what NOFOLLOW is and where it comes from. It was started by Google to fight Blog SPAM. It did not work out I might add. It then started to take new spins and created more problems and mistrust than the problem it was supposed to help solving.
See the Original Post to NOFOLLOW at the Google Blog from 2005