The Start Button in Windows 8.1 is just that, a button that takes you to the Start Screen (Modern UI, or Metro for those that tested the beta).
AFAIK, you'll be able to boot straight into desktop, which is what a lot of people are after. I do find myself going back to using start menu replacers since I often multitask and having my entire desktop in the background when I'm using the start menu is essential.
The only driver issues I had was with my soundcard, months before the official Windows 8 release. It was all mostly sorted on the launch date.
Windows 8 will never fully replace Windows 7 and there's no compelling reason to upgrade, unless you want faster boot times or will use the touchscreen interface. I suspect the next viable upgrade will come with DirectX 12, which could very well be in the distant future.
As a side note, Windows 8 is a lot smoother than Ubuntu 12.04 LTS and above on my netbook (Acer Ferrari One). I prefer Debian Sid anyway.