After playing a bit with Windows 8, the start button behavior is horrible.
This is a joke, right? I just can't imagine a secretary in a law firm being fine doing office work that way. Want to open up Excel? Sure:
1. Press start
2. scroll around in Metro and witness the eye candy
3. Forget in the meanwhile what you wanted to do in the first place
4. Getting yelled at by the boss, so you remember again and finally find Office
5. Get a headache from all the Desktop/Metro switch effects
6. Run to the toilet to puke
7. Work done
Oh, and please, please, never ditch the desktop. Something simple like opening up IE and copy and paste some text into multiple notepad windows is a gargantuan task in Metro, if possible at all.