If you reach the point where your iPhone will no longer get past the start screen, as mine did this morning, you have a powerful option. Put your iPhone into recovery mode. Here's what you do:
1. Hold down home and sleep buttons until you see the phone power down.
2. As soon as it powers down, let go of the sleep button but continue to hold the home button for a couple of seconds.
3. Once you have verified that it is completely powered down, hold down the home button while connecting to your computer.
After a couple of seconds, you will see the iTunes logo and USB cable appear on your phone. iTunes will prompt you to restore the phone. From there, you should be golden. Hope it works out!