Soft navigation keys are desirable in post-4.0 Android device... at least for some users. Some people love 'em (and curse the likes of Samsung and HTC every time a new flagship with hardware keys comes out) and some don't. For those who don't, Good Mood Droid (whom we've featured before) has created GMD Hide Soft Keys root. It's a root-only application that gets rid of the navigation bar in all areas of the device.
We've seen this implemented in a few different ways, mostly on custom ROMs like CyanogenMod, Paranoid Android, and AOKP. We've also seen similar apps in the Play Store, like full!screen.