I don't use Internet browsers very much in the office -- once in a while to research something -- and certainly not email or Facebook. I use Amazing Charts, Updox, and to some extent, Medware (though mostly the front office staff uses that). Of course those applications use the internet -- but it can't be OS issues that slow them down -- more likely the state of the Internet itself.
I suppose I can imagine putting Win8 on a home computer, but I don't see a business application.