Google will HEAVILY penalize you if they think you are doing "arbitrage" (paying for ads to get visitors who you hope will click on ads) because they think this makes for a sucky user experience. It is fairly easy for them to figure out who is doing this, considering they own the best CPC program in the world to get traffic (AdWords) and also own the best CPC program in the word to sell your traffic (AdSense). That gives them plenty of data to be a law unto themselves, but they have other sources if you decide to be tricky and try something like Yahoo CPC -> you -> AdSense.
Source ? AFAIK, google will penalize you only if the target site is filled with ads. If the target page has useful relevant content then google doesn't care. This is an accepted practice and high profile people have indulged in it (shoemoney for example) without getting penalized.
