I've used Chronos (iOS app) for a few months, and like it overall--it uses your phone's GPS ability to track where you go, where you've been, times, etc. Then you can categorize locations ("home", "work", "social", etc) and see the stats of where you've gone. The more info you feed it, the smarter it gets too.
Only two downsides:
a) it can be a battery hog, although I know they're working on this
b) I work from home--so since home + work are the same location for me, it can't differentiate the two. That's not a fault of the app though.