From a usability perspective, the start screen is faster than clicking items on the start menu. MS wrote a very convincing blog post on the matter full of statistics (which i agree with mostly). Similarly, the ribbon interface in explorer allows for quicker access.

It also has lower requirements than windows 7 IIRC, so that indicates it should be snappier, and it has faster boot times.

Vanilla Win 8 install on a bootable vhd on my notebook runs noticeably faster than a vanilla install of Win 7 on the same machine. Also, once you come to terms with the start screen just being a full screen start menu (less than an hour of use), the whole thing just kind of makes sense. I don't use Win 8 differently than Win 7, when all is said and done, other than small productivity increases from everything seeming to be quicker to find/access.