Also use "Startup Auditor", which has made a big difference in performance and battery life.
Since running these two programs (properly setup) I've kept track a few times, they have increased battery life by 2.5 hours (effective evidence).
Many programs don't just sit in memory, they connect to the network.
And how is it that I can kill apps and let the phone rest only to find more apps "in memory". I'm supposed to believe they just loaded themselves into memory and sat there doing nothing while the 3G arrows are going crazy?