Upgraded Win 8 Pro on 2 computers (my laptop [Lenovo G560] and my wife's desktop [low end eMachine, 4 years old]). And after using it for 1 week, I must say:
1. My wife loves it!!! She loves the Metro UI. Even in her machine, it was much snappier than W7. She seems to be enjoying computing more than before.
2. I missed start menu for first 4 days, but now, I have become used to W8 setting. I spend most of my time in the desktop mode, but I occasionally enjoy start screen options. Also, even in my G560, W8 is indeed much faster than W7. I don't do gaming, but use MS Word most of the time.
3. Also, I love "OneNote" app on start screen more than the one that came with Office 2010. I do some of my work on OneNote and it is an excellent app!
In sum, for me, yes, I do miss Start Menu, but overall experience of Windows 8 clearly outweighs the few negatives. I like the fact that my wife enjoys it...