I use ATK. You need to know which processes to ignore, otherwise you'll get some weird results. For instance, if you use HTC's calendar widget, which I do, and you kill the Stocks app, it'll reset the calendar widget and reload the data... kind of weird how that works. Also, if you kill the Flickr process, it'll make the UI reload. Sense is so deep within the OS that killing certain Sense apps causes weird things to happen like that.
In my own personal experience, not using a task killer makes my phone chunky after opening a bunch of apps. I've never seen the OS unload anything after a while, but then again I kill tasks as soon as I'm done using them.
None of this would be needed if all apps had a Menu->Exit option that actually releases all resources and closes the process. Some apps do have that option and they actually do close their process (using ATK you can check
)
**** My Ignore List From ATK ****
com.htc.launcher
com.htc.android.omadm.service
com.htc.android.iqagent
com.htc.wdm
com.htc.socialnetwork.flickr (Killing this causes a UI reload)
com.htc.opensense.pluginmanager
com.htc.htcMessageUploader
com.htc.WeatherWallpaper (this is for the animated weather on the home screen when unlocking)
com.htc.android.htcime
com.sprint.ce.updater
com.broadcom.bt.app.system
com.smithmicro.DM
com.android.updater
com.android.providers.drm
com.android.bluetooth
com.android.providers.downloads
com.google.android.apps.uploader
com.google.android.partnersetup
com.google.android.providers.gmail
Talk (I actually use Talk)
Calendar
Stocks (I don't use stocks, but the Calendar issue I mentioned above causes me to ignore it)
Clock (Kill this and your alarm won't go off, learned this the hard way
)