Not to be a hater, but if I was going to create a foursquare knockoff, I'd use game mechanics and create something *totally different* (e.g. the "Points 2.0" stuff we're cooking up now @ foursquare HQ).
Why would you ever just clone someone else's work? Learn from it and innovate on top! That's how we all push this space forward!
(click "All Sizes" above to zoom in)