Regarding licensing Terms
Most critical issues vis-a-vis open source licenses come into play when you cross the line from simply being a user/developer to copying and distributing. In the latter case, whether you plan to charge for the resultant product or make it available for free, is irrelevant.
I think the main concern with using ggmap is probably the licenses associated with your use of google map tiles. (Using OSM tiles would probably alleviate many of those issues) Hadley
RStudio / Rice University http://had.co.nz/