I own a Satelllite L855-11T and installed Windows 8 Pro x64 (DreamSpark full version). Everything works fine except for one thing: I can't change the screen's brightness.
I installed the newest drivers and TVAP, System Driver, etc (even from csd.toshiba.com, because these already are for Windows 8). Toshiba Function Key doesn't work, don't know why. And Intel won't let me install the display driver: my system wouldn't meet the requirements. I thought there's an integrated GPU in Ivy Bridge?
Well, when I press FN + F2/F3 the brightness indicator bar appears and changes its value, but nothing's happening on my screen. I just stays the same (seems to be applied after restart). I even deactivated adaptive brightness, but it didn't help. Any other function keys are working fine (out of the box by the way).
At the moment it is not easy to help with Win8 malfunctions. Until Toshiba doesn’t start official Win8 support we can just write about good or bad luck.
Generally speaking there are many Toshiba tools and utilities that must work together. At the moment there are no offered tested versions.
Display drivers for mobile units are offered and tested by notebook manufacturers so until Toshiba doesn’t offer it I think you should use your Win8 and learn how it works. In my opinion the main thing is to check all new functions. All Toshiba specific stuff can be installed additionally.
Later when Win8 support starts you can install it again and have well working OS including Toshiba specific functions.