WinaeroGlass by winaero is a free and portable utility for Windows 8 which allows you to enable transparency effect in Windows 8. It basically enables the built-in transparency effect in Windows and then redraws program windows quickly to make the transparency effect stable and permanent.
It also runs in background but doesn't consume much resources. Currently it doesn't have any user interface. You just need to double-click on the portable file and it'll immediately enable transparency in Windows 8.
If you want to disable transparency effect, you'll need to log off or end task of WinaeroGlass and DWM processes using Task Manager. But the developer will add a user interface to easily enable or disable transparency effect very soon.
The developer has also plans to enable blur effect in Windows 8 UI. So stay tuned and we'll update you as soon as it becomes possible.