Foursquare has joined a few other players and switched off of Google Maps and onto OSM for its basemaps. The new maps are built on OSM, but are in fact MapBox Streets, a new product from the MapBox folks, aka DevelopmentSeed.
- Foursquare Blog
MapQuest has tweeked the look of its OSM-based maps (MapQuest Open) and enhance perfomance of tiles.
We updated the styles of our Open tiles to match some of the improvements we’ve made on our licensed tileset. ...
The second change is that we upgraded the tiling platform for better performance and reliability. Hopefully it’s like a great offensive line in football – you never notice it because it just works.
- MapQuest Dev Blog