If you are on a certain data plan on your mobile provider, and don't want to exceed it, you can set data usage warning and a limit which can help you save some of your money.
If your phone doesn't want to boot up again after the update, it gets stuck in a black screen, follow this tutorial where we root the Galaxy SII with Odin and put an official Samsung Android 4 ICS on it.
Very useful Android feature can turn your Android smartphone into a Wireless hotspot that enables other WiFi devices like laptops or other smartphones to use your Android phone's Intenet connection.