I know I read somewhere that they - or so the claimed - had in mind to add premium features, but that the basic PSN would stay free.
Of course they might have changed their mind.
As I told my friends, I would probably buy a Premium PSN subscription if it's worth it.
However, if online play becomes a premium feature, I don't know if I will pay the subscription or sell my PS3s, for a simple reason: nowadays, PSN is not good enough to justify a 50+ dollar subscription.
So either they come up with a more reliable network and uber services, or I'm not paying a penny.
And even if they do, I will probably have to think about it, because even though I love the PS3 and I've bought all of their consoles in the past (minus the psp), one has to consider the fact that nowadays 360 gets almost all the cool exclusive games, it costs less and the online service seems to be much much more reliable and to have more features than the PSN.
Edit: and no I would never keep PS3 for single play. I don't even buy single player games only anymore (maybe one single player game per year).