Corporations apparently edit Wikipedia pages to portray themselves in a more positive light. See http://wikiscanner.virgil.gr/ for the scanner itself and http://www.wired.com/politics/onlinerights/news/2007/08/wiki_tracker for a story about it.
The unintended consequences here is that Wikipedia has become such a widely used a source of information that corporations are (or believe they are) affected by what it says about them. Consequently they want to change what it says. Because it's a wiki, they can. That wasn't the original intent behind Wikipedia. It's an unexpected consequence of its existence and popularity.
A broader unintended consequence of the fact that the web enables all of this is that it was relatively easy to create wikiScanner, which could bring these sorts of edits to light.