There's actually a much simpler approach for quitting apps, and that's to use your recent app list. Double-click the home button to display the recently accessed applications. Press and hold any of the icons shown, then navigate to the application you want to quit and tap the red circled minus button.

via www.tuaw.com

Useful to know – this had been bothering me since I struggled to get the TomTom app to go away once I arrived at my destination…