We will see some paid models take off now as people are tired of in your face ads all the time.
Here's how I use social networks:
Facebook: has everyone I know well or am acquainted with. good for looking up contact details/current status. good for updates on bdays, anniversaries, graduations etc. (free is good)
Twitter: Best way to get breaking news on stuff I like and stuff in general. I retweet things I think are relevant, easily the service you would use to get to know me. (would pay for this)
Google+: Like it for the nerdy and geeky posts and cartoons :) (free is good)
Email: besides work stuff, long email threads [gmail creates a new thread after 1000 emails] with close friends/family about personal stuff. (would pay for this)