I heard it's OK, my friend actually have an account. It have some nice features and advantages like "Hangouts", but it's in the big shadow of more popular Facebook, Twitter and MySpace. Hardly that would find it's place on the market.
I joined it, but stopped caring the same day. What's the point of a social network site that only has a few people you know? If it ever overtakes facebook I'm ready, but for now I don't use it at all.
I have an account, but haven't logged on in a few months, don't even know anyone who has it. Created an account to see how it looked, plus I used it to waste away a work day by playing the games there..