For the next week, Instapaper for iOS is available for free as a part of Starbucks' "Free App of the Week" campaign. To get your free copy of the app (which normally costs $4.99), you have to physically go to a Starbucks shop and get a promo card, then enter the code into iTunes. This is a big week for developer Marco Arment — Instapaper launched on Android earlier this morning, and the iOS app was recently updated with support for background location updates. In his Build and Analyze podcast, Arment mentioned that while there are several thousand promo cards in circulation, even he doesn't know the exact number, so it's best to act fast if you want to drop $5 on a coffee instead of the app.