iOS 7 App Switcher Tips and Observations
When swiping across app screens (vs icons) tapping an app screen stops the motion, but tapping an icon opens the app. Likewise when swiping icons: tapping icons stops the motion, but tapping an app screen opens the app. Knowing this allows you to switch apps faster.
Triple-tap Home to peak at the most recently-used app.
Also, it appears that some apps are able to live update their app screens in the app switcher. Perhaps the ones that support the new background update API?