Pinterest isn't even publicly available yet. Maybe the fact that someone cloned them so quickly will make them get off their asses and make it available to everyone.
'Not being public' is an 'exclusivity club' ploy to make new members want to join and be apart of the fun.. The Winklevoss Brothers' idea of exclusivity for Harvar / .edu emails helped Facebook similarly with initial growth.
Yep. It's cheap and stupid. Why bother waiting for my pinterest invite when I can sign up for pinspire right now?
Given that network effects are most important for a startup like this, it's quite possible that the clone can overtake the original in a short amount of time.