Return to desktop after closing an app
Solution 1:
Note: This is related to Windows Store (Metro) apps. Desktop apps don't follow this paradigm.
The mindset that Microsoft is trying to implement through Windows 8, is for the user to not be concerned about closing applications all the time. Memory, CPU and other resource usage is handled dynamically by the OS (similar to Mobile OS's). This is handled through an application lifecycle:
With that in mind, closing the app shouldn't be done unless absolutely necessary.
To go straight to the desktop from a Metro App use the Win + D keyboard shortcut.
Solution 2:
The argument against "don't close your apps" is when you have 20 apps open, and you try to Alt+Tab or use the App bar (swiping in from left), it's very cluttered if you have 6+ apps open.
I have found a solution to this problem (return to desktop after closing an app), but it uses a program that costs money (only $4.99, free trial available). It's called Stardock "Start8". It's main use is to give a Windows 7 start menu on Windows 8, but you can return to desktop after closing an app without doing that.
When you install it, change all of the settings however you like, and on the "Desktop" tab, click the "Advanced" button. Check the box that says "Return to desktop after closing a Modern UI Application". Done!