Yelp iPhone app gets Foursquare-style check-ins
Certainly, Yelp won't be as robust a game as Foursquare or Gowalla ... at first. People are going to have to rethink their Yelp friends lists in light of the additional privacy most people demand when they check in to locations in real time.
Someone who writes good reviews might not be someone I want to know my whereabouts all the time. Yelp also needs time to build badges - so far, there's only one, for being a regular at a venue. It's nice to be able to see that a reviewer actually frequents the establishments he's writing about, but Yelp will have to step up its themed badges to compete with Foursquare.
On the other hand, if huge numbers of existing Yelp users decide to embrace check-ins, it could be game over for Foursquare and Gowalla.