Phone trouble happens all the time, but there are some situations that are far worse than others. A friend's iPhone completely refused to turn on recently, and after the initial freak-out of having no phone, she took it to the Genius Bar to be repaired. Luckily, her phone was salvageable, but only after a factory reset, which completely wipes out the phone's data and restores it to factory settings.
As long as your phone's data is backed up on your computer, much of it can be restored. But there are a few things that could prove tricky to recover. If something like this happened to you, what would upset you the most?