Or, to properly kill a running app, hit the X in the lower right, an action that feels a bit ornery compared to the fun of flinging an app that you no longer needed off the top of the PlayBook's display.
It also increased my confidence that Twitter will be successful in its mission to kill off some of the most useful Twitter-app makers and provide those apps itself.
If you're traveling and expect to use Maps to navigate, Google to scope out enjoyable things to do, your email app to keep in touch, Instagram to brag, Foursquare to keep tabs, Facebook to kill time and your cloud drive of choice to sift through flight and hotel confirmation PDFs, it'll be dangerously easy to exceed 100MB in a day.