Yelp (YELP -2.2%) is off following the release of Google's iPhone Maps app, which stands to hurt the use of Apple Maps (and with it, the Yelp content that's integrated). Also possibly hurting Yelp is a TechCrunch column noting signs Apple is cozying up to Foursquare, which is increasingly stepping on Yelp's turf. The article speculates Apple could ditch Yelp for Foursquare. However, while Foursquare has more check-in data, its U.S. reviews content doesn't compare with Yelp's. JPMorgan upgraded Yelp yesterday, arguing it has only 36K local advertisers out of a U.S. base of 27M+.