Also, you have to remember that:
- Automatically running task killers that repeatedly kill tasks are simply gonna kill your battery - especially as those tasks keep trying to reload and your app keeps trying to kill them.
- The new FroYo comes Overclocked just a bit - but just enough to make a difference - not the only reason, but a contributing factor as to why your battery life is going to be a bit shorter than before
- All your apps were installed under 2.1 - and 2.2 has some very different coding in it, so that some (perhaps quite a few, or even a lot) of your apps will be better off being reinstalled - which a factory reset will help you achieve.