i left my job with no savings and intending to do the same thing, because i was just not happy with my position at my new employer.
within three months i was completely broke, but with a github account with hundreds of commits.. and then my old boss from my second-to-last job called, and offered me job back, at a huge raise, and allowing me to work remotely, and pursue my own codebase/startup dream on the side.
quitting for the right reasons can have wonderful side benefits. :)
personally, i find foursquare, gowalla, and the like criminally useless.
the aggregation of all this location data and the sum result of either sharing your location with your friends or seeing an absolutely barebones of the establishments around you, without any context, doesn't result in a useful experience for me, at all.