The latest version of the Apple iOS software has been released. You can download it over the air (OTA) if you are on wireless & have more than 50% of your battery remaining. You can find it under Settings > General > Software Updates.
This version is to support the latest iPad3, as well as fixing some bugs. 5.1 is pretty stable, and everyone running an older version of the software should consider upgrading. Here is the screen of our iPhone, saying that it’s 189MB small.