Steve Rubel recently posted on (what he considers to be) the influence of Wikipedia wrt brands on the web. The basic point he wants to make is that search results for a certain set of brands often include Wikipedia results and so Wikipedia has a lot of influence. He further notes some entries which contain potentially damaging content about brands.
However, Graywolf followed this up with a look at the click through rates for searches on these brands in the AOL search data and found that people don't generally click through to those results. It isn't too much of a stretch to then claim that Wikipedia actually doesn't have any influence - perhaps people see the result and decide not to go there due to some preconceptions regarding the content found on Wikipedia.
I suspect that part of the problem here is a lack of understanding of intent: search engines, due to their narrow interfaces, have no ability to disambiguate intention. If searches for a brand were intended to find items for sale, for example, Wikipedia would not be a good result. If they were intended to find blog posts or reviews, again, Wikipedia would not be a good result. If, on the other hand, they were looking for historical or other factual information - no problem.
[Via Emergence Media.]