[citation][nom]nebun[/nom]from the way it looks, win 8 is more like a service pack....[/citation]
Sure, it is based upon the same general OS idea of Win Vista/7, but there are so many changes, improvements, and optimizations that it really runs like a whole different animal. You won't notice the difference so much on a desktop, but the difference on a laptop is astounding! My netbooks both run much smoother with win8, and they got a sizable increase in battery life (less HDD reading, less wifi use, less system overhead on the CPU and Ram all adds up). It is a true leap forward on the technical level, while still providing great backwards compatibility (for the non-ARM version anyways).
The only issue to take with it is if you like Metro or not. Personally I am not a huge fan, but it is not bad either (especially once you have logical program groupings/labels, and link to your social media accounts). After using it a while I find it much more interesting/useful than the old start menu, and I also find that I simply never see it in day-to-day use (which is all in the desktop environment).
Yes, there will be a learning curve, and it will be painful, but at the same time I think it will be much less of a leap as it was moving to win95 (which was broken until win98SE), WinXP (which was a cartoonish resource hog and 'required' 1GB of ram to run smoothly when 128MB was still the norm), or Vista (which was another huge resource hog, and 3rd party hardware developers had terrible driver support, especially for the 64bit edition). Win8 runs smoothly and stable on just about anything, is much smaller in size, and is fairly intuitive once you get the idea of what they are trying to do with Metro.
So ya, there will be some preference issues with the new OS (it amazes me how much zeal people have for the Start Menu, but then again I have used several OSs over the years, most of which did not have a start menu), but to say that it will be the nightmare that some other 'upgrades' have been upon release is a bit of an overstatement. I mean, there is nothing worse than an OS that is simply broken, or where 1/2 of your hardware does not work properly for the first 2 years of use. My bet is a 1 year adjustment period, and then everyone will get over it and begin to move over.
One thing is for sure; It will not be the train-wreck that Vista was.