Do you want to become a stumbler?

I am sure that there are millions of people out there that already know about this website – http://www.stumbleupon.com. But I just stumbled upon it this morning. I am now trying to figure out how people could leverage it as a marketing vehicle. The concept is so simple and logical, I am amazed that Google hasn’t already done this, or at least bought this company.
StumbleUpon lets users – called Stumblers – give the thumbs up or down on content they find on the net. Stumble builds up a profile of a user’s likes and dislikes and matches other content around the web to their viewing habits.
I am going to join up and start using it, and will post more in the future about what, at least on the surface looks like an amazing site.
If anyone out there has experience with it please post in the comments!