A lot of it has to do with internal memory, and cache
I've been having problems with it lagging and freezing lately too. I'll be in an app, usually the Amazon Appstore or the Android Market (though it's happened with others) when the touch screen stops working and the bottom four buttons become unresponsive. Turning the power button on and off again gets it working again. It's wierd because I've never had this happen with any previous smart phone.
I understand it is like a computer, and a hard reset may do the trick for a fresh start, but it's still odd that it is doing this when it isn't even 6 months old yet.