Real competitor to Facebook and Twitter? (G+ doesnt count)
Firstly, Google+ was forced upon us, but nobody uses it, so don't start.
I run a big music & entertainment website at onedirection.net and up till today I've only ever saw the need to include Facebook, Twitter, and yes Google+ buttons, as they're the big three.
Pinterest has grown so fast though out of genuine word of mouth. Its a site that people like, and its a great alternative to both FB and TW. So much so that Ive now added a "Pin This" button on the site.
Guaranteed, we're seeing a viable new entry in the social media market here, not just an over-inflated-about-to-burst one.
And its quite cool too. Give it a go.