I recently read that Sony would be using GameSpy technology in their network (I'm not sure to what extent, and I dare not ask anybody with an NDA hanging over their head).
I follow up (in a roundabout manner) with this issue in a topic on GameSpy Forums, found here. [GSI] employees talk about how things work there. Admittedly, there's no tough questions asked - it's pretty much just playing softball, but again, the NDAs. I do think some folks might find their repsonses interesting (and funny, as well).