Little Gain for Business
The move from ME to NT/2000/XP could be justified, better stability, 32 bit and all, but there's just no really good reason to go Vista and, to be honest, Windows 7.
I suspect Windows 7 will gain from not having the Vista name attached but it'll have to pull something more than that out of the hat. There should be some traction from the move from 32 to 64 bits (especially for servers and gamer rigs with massive video-card memory) but its nowhere near the impetus that the move from 95/ME had. Any business which reckons it generally needs more than 4gb ram on the desktop needs to have its IT policy and practises scrutinised.
With Apple doing better than it did, MS is really caught. There are a lot of people out there who aspire to have one of those low spec Macbooks rather than a "better" Dell or HP laptop. For MS, that's a big "ouch!"
Vista is pretty much dead in the water as W7 is rushed out, but in the meantime, with every "I don't care about computers I just want to do stuff" new home Macbook user, MS gains a "my pc at work sucks" user. From the other side, KDE 4.2 (just for example!) brings Mac-like eye-candy to the standard pc and provides the computer enthusiast with tinkering to their hearts content.
Of course MS will do well with Windows 7, but if they want to keep ahead of the game, they need to pay some serious attention to what customers actually need and they need their hardware providers to do something really quite special to make the Windows PC something someone, anyone, actually wants.