One of the authors of Checked-In Discusses Foursquare marketing locally in the Palm Beach Post Techtonic Blog.  The article can be found here:

http://blogs.palmbeachpost.com/techtonic/mobile/local-and-national-companies-experiment-with-foursquare-marketing-with-varied-success/

We are pleased to launch Checked-In the first book dealing with Gowalla and Foursquare!