CNET News.com reports: "Microsoft has confirmed that all versions of Vista will be shipped on a single DVD, in a feature called Windows Anytime Upgrade. ... The idea, said a company representative, is to let customers more easily and directly upgrade to a higher edition of Windows Vista from within their current edition. Vista is scheduled to reach consumers in January."
Personally I think this is a great idea. I don't know how many times I had to search for the right CD (i.e. Windows XP: Home, Professional, Media Center, Tablet, x64) when I needed to build a system, add a new component, etc.
Plus the idea of 'Windows Anytime Upgrade' will definitely be a welcome feature. For example, lets say you just bought that new PC, and it comes with Windows Vista Home edition, but you really wanted Ultimate edition. You don't have to buy a new copy of the OS (which can be expensive), you just have to pay for the upgrade price (which is cheaper then a full copy).