The iPhone Dev-Team has posted following the release of iOS 6 to detail which devices can be downgraded from iOS 6.x to iOS 5.x and which devices can be re-restored.
Rather than using a CPU core based on a vanilla A9 or A15 design from ARM, Apple is reportedly using a custom core for the new A6 SoC found in the iPhone 5.
A video recording app, Flexicorder allows both front and back cameras for iPhone 4 to be used during a single recording session leading to some interesting possibilities.