iOS (Jailbroken): As Addictive Tips points out, the visible-only-when-necessary keyboard on iOS devices comes with a dismiss button on the iPad, but not on the iPhone. This behaviour is fine most of the time, but I'm sure you've run into certain lousily-coded apps that cover up important information with the keyboard even when you're done typing. Pull to Dismiss solves this problem.
You get Pull to Dismiss the same way you get other Cydia tweaks, provided you've already jailbroken your iPhone. Once installed, all you have to do is swipe down on the keyboard to get rid of it. Very handy when you're trying to access some region of the screen where the keyboard is taking up space, or if you're in a text editor and all you want to do is read, not write.
To get it, search for Pull to Dismiss in Cydia.
Quickly Hide iPhone Keyboard With Pull To Dismiss [Cydia] [Addictive Tips]