I just read, by chance, a very interesting essay a Wikipedia administrator wrote in his personal page. It deals with people spamming or vandalizing Wikipedia, for fun or for personal promotion/economical benefit.
I'll quote the intro paragraph:
Let's face facts: Wikipedia has become an important force on the Internet. If you've got a business to run or a belief to circulate there's a big temptation to hit that edit button and do your thing. You're on your honor here. Most people have honor, which is why Wikipedia is huge and (usually) pretty darn good, but then there's that thought - what if you could harness this site and make it work for you?
You aren't the first person to get that idea. And hello there, I'm a Wikipedia administrator.
Read more in the whole essay.