[idlehands]

akulbe has hit a couple of important points. Just because someone thought of something, or even made a thing, doesn't mean they own the idea. If you copy their exact execution, shame on you. Otherwise, go for it. On paper, any social network is the same thing. But we don't use friendster anymore.

IF it seems appropriate to give credit to someone else for inspiration, go for it.

Just remember, the market will determine the winner. Effectively, that's really all that matters.