Being an international customer, it's clear 50% of the features aren't available, as with any platform - developers build even showed this, quite pathetic.
It needs the A5 processor to run, so can't run on any older iPhone models. As far as I'm aware it will also not run on the iOS5 update on the iPad 2, but I will be able to confirm this shortly.
Quite a few of my friends report back to me that they get errors during the initialization process of the phone. telling you to reconnect to iTunes, even though it is, and you have to start the whole thing over again. One person had to restore to factory to get access to the phone again.