I found out about the whole 40 dollar upgrade promo..and I figured I'd go ahead and buy it before it goes up to whatever absurd price it will be after January. I can't find a link or anything to preorder, is it because Windows 8 hasn't been released yet?
I think it is an upgrade install as opposed to a full install so it should not destroy all your files. This link is regarding the release preview version but if you look at the upgrade section/question it says you can keep your files and even programs if your upgrading from windows 7.
For the $40 Windows 8, you can only download it starting Oct 26th. I called them and they wouldn't tell me how long that offer is but I found several articles that mentioned Jan 2013. They also told me it was a full version but the guy I talked to didn't know what Linux was so it may have been a wasted phone call.