I recommend using Android Assistant. It allows one to monitor CPU usage, Memory usage, Battery usage. It shows what process is currently active. It has Quick Boost feature that releases memory from inactive Apps. While in Android Assistant, use Menu -> Settings -> Auto Boost to release memory. Set up Auto Boost Frequency in this Menu. Also, in Ignore List select Apps / processes that need not be killed periodically by Android Assistant. There is option for User Apps and System Apps/Processes to be ignored for periodic killing by Android Assistant.
Also, Go Launcher Ex Home Replacement App allows to find Running Apps and then gracefully Close the ones that are not needed.
Phone can become slow if there are many Apps running that need a lot of CPU power and do a lot of I/O to phone storage such as MicroSD card or SQL Lite Database. Phone can also become slow if it is brining a lot of data from remote location over phone network or sending data to remote location over phone network.
I agree that we should not kill processes as there is danger of we killing the important and needed system processes/apps.
