This is interesting because maps are obviously a vital part of location-based services. And while a few have picked Bing Maps over Google Maps, I can’t recall any service as big as Foursquare, which was using Google for so long, ditching them in favor of the open alternative (as they note, several smaller startups have, often due to cost — which was also why Foursquare started looking for other alternatives).
Worth noting that this only impacts the Foursquare website right now — the iPhone and Android apps will continue to use Google Maps since both of those OSes offer Google Maps in their SDKs.
But that brings up something else: how long is Apple going to stick with Google Maps? At the time of the iPhone launch, it was really the only good solution (and they had a great relationship with Google). Now there are several options (and the Google relationship has gone to shit).
I think it’s quite possible that the only reason Apple hasn’t switched to another alternative at this point is because they continue to work on their own solution.