Jaimie Sirovich has made a (belated) post about Wikipedia nofollowing all their outbound links. I never commented on this issue when it first arose, but Jaimies clever title brought his article to my attention. He suggests that Wikipedia nofollow outbounds for the first 90 days. I think this is a bit silly as Google et al can currently decide the age of a link and weight it accordingly should they decide to do so – and Wikipedia and other sites ‘aging’ links on-site would just complicate matters even further.
No-one seems to have realised that Wikipedia is worthwhile spamming for traffic alone never mind PR, so the spam ain’t going to stop.