What is the difference between the ad networks and the companies being advertised by the spam? It is only one level of accountability away and if MySpace sent cease and desist letters to those companies, I wonder if they'd sue those companies too. That would be more scary for the future of affiliate advertising of those companies had to take responsibility for affiliates marketing their campaigns.
On the good side for aff networks, they could possibly make the argument that MySpace has the ability to stop spam on their networks with little technical difficulty by evaluating and deactivating links resembling affs in bulletins. Could accepting and remaining someone's friend in myspace be opt-in? This makes me wonder if theres a way to eliminate aff ids and completely conceal the affiliate relationship.