As you know, Wikipedia nofollows all their external links, so links from Wikipedia should have no impact on your rankings - be it positive or negative.
A WebmasterWorld thread have some SEOs disagreeing with that.
Some are saying because there are so many Wikipedia scrapers out there, when you get a link from Wikipedia it can hurt you.
A Junior WebmasterWorld member explained his case:
My recently relaunched website has been featured in Wikipedia as a 'resource' on a very relevant page. I have no idea who did this but I was obviously thrilled at first that somebody felt my website was relevant enough to appear there.
This seems to have caused no end of problems on Google, however. Because my website's brand name is also a popular keyword in its niche (it is an EMD, but a short one) that is the keyword that this indivudual used on Wikipedia. My problem is that there are dozens if not hundreds of websites that scrape Wikipedia and now my keyword appears as anchor text on those websites.
It seems that Google has penalised me for this because from their point of view they see dozens of links with the same anchor text. Because my website is relatively young this makes up a large proportion of the link profile and I don't think this looks natural.
I guess if the scraper remove the nofollow and if the site has very other links to it, outside of the scrapers, I guess it can hurt.
But this all seems a bit farfetched and I suspect there is some other issue.
Forum discussion at WebmasterWorld.