Foursquare is a hot topic these days. Another article about using it to boost business.
http://smallbiz.att.com/OSB/Idea-Exchange/Experts-Detail.page?type=LiveSite:News&dcr=templatedata/LiveSite/News/data/How_to_Use_Foursquare_to_Boost_Business.xml&contentId=g8f4ya7i