Back in September 2011 I wrote a blog post called Windows 8–Why you don’t close a Metro Style application. Well with the Consumer preview things have changed because now you can directly close a running Metro Style app without going through the task manager.
In the below example I have started a few Metro Style apps and have just switched back to the Task manager,
On the Metro Start screen or Windows Desktop when pointing the mouse to the upper left corner it will first display the last used app, when moving the mouse down (keep the pointer at the edge of the screen) any other running app will appear as well.
A right click on an app will show the “Close” option, allowing a user to directly close the app.
So for all that had worries about ever running apps in the background, you can now if you wish close the app.