The problems that come up with the iPhone 3.1 update are somewhat strange and unexpected. There are a number of shutdowns that may occur and iPhone's have been known to freeze spontaneously. The iPhone is not always the most stable portable, but with this you can expect even more applications closing and problems with general function. There have also been reports that the iPhone's battery life has been affected, though this may or may not have any truth.
Though the firmware can affect the iPhone's battery life it is not a concrete connection. There is also an occurrence of "Unknown error (-50)". Overall, the iPhone becomes slower once the iPhone 3.1 update comes in, though this is only in some reports and not conclusive for all. Once thing that is universal for the iPhone 3.1 update is that Podcasts getting a random ordering.