Windows 7 - Explorer.exe not shutting down

When I open an instance of windows explorer to manage files or start a video (or anything for that matter) and exit from it, the task manager will show that it is still running. Since I rarely reboot my computer, after a few days I have to go into the task manager and shut MANY instances of explorer.exe down manually. I usually just leave the one consuming the most memory running since this is usually the one managing the desktop/taskbar. Has anyone else found this to be a problem for them? The number I have to shutdown has exceeded a dozen before, it gets crazy.