Not a huge surprise, I suppose. Google's ad network is still the market leader. Though, I am very interested to see how much more relevant Yahoo's Search Marketing has gotten with its implementation of Pandora.
So far, AdSense is the most flexible when compared to Yahoo's Publisher Network but there are many more players in this game now.
To be honest, I was surprised Google reached out to Friendster. Google struck a similar, but much larger, deal with MySpace, so I imagine that this won't go lightly with NewsCorp. Let's not forget that Google also owns two major MySpace competitors, YouTube and Orkut (see Orkut's astonishing growth: http://www.alexa.com/data/details/traffic_details?q=&url=orkut.com/).
Is Friendster even worth risking a major deal with MySpace?
As you pointed out, Google already competes both directly and indirectly with myspace; NewsCorp knew that going in, and went with Google anyway. I doubt that serving ads for yet another social network would be enough to drive NewsCorp away--and I even more seriously doubt that their contract with Google would allow it.
One point about Orkut: while its growth is phenomenal, most of that growth is in non-US markets, so it does not pose any direct threat to either Friendster or myspace.
So far, AdSense is the most flexible when compared to Yahoo's Publisher Network but there are many more players in this game now.