I think it's questionable whether there will ever be a new desktop operating system from Microsoft, at least as we have come to think of operating systems as being a singular product. It took five years for Vista to come out. In another five years, I think the operating system on an actual computer will be less important. Although we have been able to see this theoretically for quite some time, it is starting to become an actuality that more advanced operating systems are being used on cell phones and televisions (iPhone and Apple TV).