At the end of the day, 'nofollow' on wikipedia
has little effect, since
as Betacommand points out on Wikiproject:Spam:
"Once our mirrors and scrapers get a hold of it, most drop the nofollow
thus the spammers do get rewards for their actions on wikipedia."
Why would that result in little effect? It has been a while since I've
played around with the math, but since Wikipedia has much higher
PageRank than the mirrors, it would seem like our nofollow would still
make a big difference in PageRank bump for the spammer sites.