Do I really need to install a task manager? Does one really need to install a task manager? My phone does slowdown on rare occasions but it's not something that hampers regular usage.
See this 

http://geekfor.me/faq/you-shouldnt-be-using-a-task-killer-with-android/

FAQ: Why You Shouldn’t Be Using a Task Killer with Android (geekfor.me) - xda-developers


  tl;dr version:
  
  
  Android is hard coded to automatically kill a task when more memory is needed.
  Android is hard coded to automatically kill a task when it’s done doing what it needs to do.
  Android is hard coded to automatically kill a task when you haven’t returned to it in a long time.
  Most services (while possibly running in the background) use very little memory when not actively doing something.
  A content provider is only doing something when there is a notification for it to give. Otherwise it uses very little memory.
  Killing a process when it isn’t ready only causes it to have to reload itself and start from scratch when it’s needed again.
  Because a task is likely running in the background for a reason, killing it will only cause it to re-spawn as soon as the activity that was using it looks for it again. And it will just have to start over again.
  Killing certain processes can have undesirable side effects. Not receiving text messages, alarms not going off, and force closes just to name a few.
  The only true way to prevent something from running at all on your phone would be to uninstall the .apk.
  Most applications will exit themselves if you get out of it by hitting “back” until it closes rather than hitting the “home” button. But even with hitting home, Android will eventually kill it once it’s been in the background for a while.
  


As Android was designed you don't need to kill apps.