This is exactly my problem with gesture based interaction, especially on the iPhone (I don't know if it's better on Android). The gestures are almost always not obvious. There's simply no hints that their are available or what swiping the screen in circles and flicking the home button might do. It may get you one step back in your browser history, it may do nothing.

That would be fine, if gestures where complementary to on screen navigation, but often the gestures are the primary "UI".