MongoDB has become an internal favorite here at Modondo. MongoDB is a great document database that can be used for many things. We at Modondo use it as the main storage engine for two of our core products and several labs projects.
In a current project that we are working on. One of the requirements are to be able to search the database for various locations and then list the items found within these locations on a map. Now both MySQL and PostgreSQL have support of geospatial indexes and the current solution are using MySQL.Mas:

http://blog.modondo.com/2011/08/using-mongodb-for-location-based-and-other-geotargeting-services/