Time is money, and apps don’t last forever. You’re never going to get back the hours you spent Oinking that hip record shop in Williamsburg or Stamping the bars with the best absinthe martinis. The weeks you’ve spent carefully crafting that ‘Slow Jams’ playlist on Spotify binds you to it, and discourages you from switching to Rdio or Rhapsody at the bat of an eyelash. If Apple acquired Foursquare to supplement its lackluster Maps app, it could, in an instant, render void your hundreds or thousands of check-ins.Free apps are dangerous, yet free is the dominant business model most mobile apps are taking these days. The roadmap is simple: grow as