Foursquare has been able to compete with Facebook Places despite Facebook’s large user base, two reasons I believe are that Foursquare was able to associate itself with the whole “checking-in” phenomenon at the same time unlike Facebook Places, I can re-visit the places I visited, tips etc.
Groupon has a similar advantage over Facebook which they need to leverage. Their expansion into India, Israel and South Africa is smart use of the $950 Million investment. An excerpt from my post about Groupon’s expansion:
Groupon’s expansion is crucial since it is fairly possible to assume Facebook’s interest in the market segment. Facebook has a large (social) user base and with products like Places where they are partnering with local stores it won’t be a surprise if we saw Mark Zuckerberg announcing a service that will allow you and your friends to buy coupons to products based on your interests. With the amount of data that Facebook mines through finding similarities between your friends and suggesting offers is within the realm of possibility.