Hey guys, I'll chime in even though I'm a new Android/Smartphone user. The reason I think I can help out a little is that since I've upgraded to the Samsung Epic on Aug 12, 2011 is that this phone has been nothing but a headache from day one and I've been through 3 phone exchanges to day. Sprint tech support has 90% moron's who have less of a clue than I did so I finally gave up on them and came to places like this and did my own research and experimented on everything. I still have some issues with the phone but I've gone from a 30% stable phone to over 70% stable phone so I've learned very quickly about my phone and what seems to work and what doesn't. No expert but I had to grow up quick so to speak.
Anytime I have an issue with the phone running sluggish the first thing I do is reboot. I've tried shutting down 1) holding the power button, 2) taking the battery out, and 3) holding volume button, power button and camera button at the same time which causes a quick reboot.
For a sluggish phone I just do a quick reboot, (3 button restart).
Problems with apps working, namely in my case the Marketplace, (Pull the battery, wait about 30 seconds then put battery back).
I stay away from Task killers myself. What I do use are cache cleaners. You can clear cache's through the "Manage Apps" in settings and do it one at a time or you can use an app that will let you choose which files to clear the cache on. I have found that some apps just build up a heavy cache load which seems to affect performance. The big one's are things like web browsers, facebook, twitter etc. I just use a free app called "App Cache Cleaner" by Infolife LLC which is free. You can tap it to clear, open the app to clear or set up an interval to do it automatically.
I'm always testing an experimenting with my phone so I constantly have to reboot, reset my phone but things seem to be running much smoother since I stopped asking for Sprint's advice. Hope this is some help.
Jim