One common problem is that the device becomes totally unresponsive to any form of input. This is called "coma mode" in jest, but a quick re-boot will usually get the phone to start up again. However, one iPhone user posting on the Detroit News forum wrote how he reset the unit to factory settings, restored it, deleted his email account, set Autolock to "off" and even removed all third party apps in an unsuccessful attempt to stop his phone from these random shut downs. He wanted to go back to using OS 3.0, but iTunes does not offer that choice.
This is not a case of a small number of people just trying to stir up trouble. Phones Review did a survey and asked readers if their iPhone was useless after downloading 3.1. An incredible 70% said "Yes". And even those who still have their iPhone functional after the new upgrade are complaining about the battery and uneven Wi-Fi support. Is the 3.1 upgrade the buggiest iPhone OS ever? For the sake of iPhone users and Apple fan boys, let's hope so because that would imply improvement for all future builds.