Google just went live with Google AdWords/AdSense ads on Myspace.com. It's part of the search network, so if you're an AdWords advertiser you cannot opt out of your ads appearing on MySpace:
MySpace Search Traffic
Google’s AdSense for Search has gone live on MySpace.com. Clients currently running ads on Google’s Search Network are now eligible to have their ads served on MySpace.com searches for US-based traffic only.
This is big news, as I don't expect any of this traffic to convert very well, but who knows? It's also important to note that you cannot opt out of this.