Am I new to the world? Nope not at all, but if you're going to point the blame then so do it, you won't get anywhere.
If hundreds or thousands of people are having the same issue then were are they? I can only see a handful in this discussion forum, it seems as though there are a minority with issues with the SW Update including yourself and you CANNOT blame 3.1 update because you have to consider many possibilities before making assumptions:
--- iPhone is slow? How do you charge the battery? It's like having a TV remote control with low battery it will be slow to respond, change the battery and it will have a high percentage of working better. In the iPhone's case, calibrate the battery as it should be charged, once it reaches 5-10% charge for 2-3 hours and repeat this process to calibrate the battery.
--- Disk space, how much is left on the device?
--- What steps have you tried to perform to resolve the issue? You ask if I was new to the world, even if I was I'd make sure to follow Support Articles provided by the vendor to help resolve the issue...
--- And yes a Reinstall of the firmware is an easy option, obviously if you are not comfortable with performing this step as suggested and will be suggested by AppleCare Agents then there is no point whinging about this issue, no offence but I'm only trying to help people as much as I can here but there is no official evidence that the 3.1 upgrade is the exact cause here, if you can determine any better then I'd like to hear your suggestion otherwise there is no point flaming when someone needs assistance...