See the FCC announcement here.
MapBox has been winning a lot of high-profile converts lately, such as Foursquare. In my opinion, it’s one of the more perfect web mapping solutions, commercial or open-source, to come along in a while. The combination of cartographic engine (Mapnik), tile generation (TileMill) and storage (MBTiles) make MapBox one of the most elegant ways to serve beautiful maps currently available.