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 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..