c|net has a set of interesting pages on various trypes of social software, including wikis, tagging and maps. Definitely worth a look.
Online mapping is evolving into a historic nexus of disparate technologies and communities that is changing the fundamental use of the Internet, as well as redefining the concept of maps in our culture. Along the way, map mashups are providing perhaps the clearest idea yet of commercial applications for the generation of so-called social technologies they represent.
They are, in a very real sense, bridging the gap between the virtual and physical worlds.