Most of the maps used with Leaflet.js maps are based on OpenStreetMap, a freely editable and freely usable source of map data. Although major companies such as Google and Microsoft produce maps, free information gives OSM an unparalleled level of detail and customization.  This year, Google has begun charging many of their Maps users, and has convinced several sites to switch.

In the past few weeks, Foursquare announced they would be switching to an OpenStreetMap layer from MapBox.  Then Apple switched maps on iOS's iPhoto app to their own system, partially based on OpenStreetMap.

Follow the #switch2osm hashtag on Twitter https://twitter.com/search/%23switch2osm to read about other websites changing over.

Will OpenStreetMap catch on? An apt comparison has been made to how Wikipedia's free-form, freely-editable articles displaced the Encyclopedia Britannica and Encarta. It was free-er, it was cheaper, and it made sense.