Task Killers have been known to be another app running in the background for no reason so you have to terminate it too after you use it. Your best to uninstall most unwanted apps. If you are rooted then install a removal app. Ther be many things you can remove, so far I have removed the following apps;
Key Chain
Swype
Sprint Zone
Self Service
Sprint Permissions
Sprint Touch Management
Touch Pal Spanish
Browser
Sprint Installer
Media Share
Market Feedback
Sprint ID
Google Play Movies
Messaging
Google Play Music
Google Play Books
Google Play Magazines
With no Ill affects
You can also stop the Google play from updating in the menu. Got sick of it updating the same apps every day.