I really think you should visit the thread in my sig, which is stickied as well.
You have told us nothing to go by though...
Rooted?
ROM?
Kernel?
2.1/2.01/2.2?
Possible update refreshes like calendars, Facebook, etc...
Maybe the 2.1 update as of recent is trying to push to your phone but OTA certs aren't there...
We need more info - and if you need basics on kernels, heat, and battery, I suggest you read up as there is tons of info and threads on these subjects.
Nick