It's inevitable, right? The things that start out small but grow because they're actually popular (aka movements) and then they get exploited for less authentic reasons (aka campaigns).
Example? How about the recent Paris Hilton contribution to You Tube? It's a pretty clever move by her publicity machine to reach out to a massive audience outside the mainstream media. But, it's also what's called astroturfing - planting a manufactured piece into a more organic environment. Of course, it's happening everywhere, like with the new teen flick 'John Tucker Must Die', having its own space (aka being marketed) on MySpace. Of course, MySpace also proved to be too commercially viable to be left to its own devices and it was swallowed up by News Corp. Too much ad revenue to resist for Rupert!
It's not like this is new - there have been fake film critics reviewing movies, "news" stories that are spoon-fed promo pieces and more - but what's interesting about the Internet, of course, is that access to audiences is no longer mediated by a third party - no media owner or journalists in the way. There are no gatekeepers (that's a whole other blog!) and so it's complete market access for advertisers.
More and more, you're seeing advertising diverted from network TV to specialty TV channels and the Internet. I'm not suggesting that using sites like You Tube and MySpace for commercial enterprise is wrong in anyway. Not at all. It's only my suggestion that capital flows like water and it doesn't really know boundaries. When a new space opens up, capital will flow in and, usually, change things.