I still remember back when Digg was a powerhouse. They came out with an update that dramatically altered their ranking algorithm.
The change had to do with looking at how often the exact same people "dugg" the exact same articles. If people very often dugg the same things, then their votes began to count for less.
It doesn't take a rocket scientist to figure out that Google will probably be doing the same thing. That means that when you're buying those +1 votes you need to spread around who you use and when.
Further, just like Google is doing today with Places, I am certain that Google is going to be expecting a variety of different types of media engagement.
In other words, if all you get is +1s Google will find that strange. If all you get is facebook likes, Google will similarly find that strange.
My point is to make sure that you get a little of a lot of things from several different sources.