I bet it will be faster replaced by its successor than any other Win version to date, including Vista.
It will also continue the tick tock trend started by Win2000:
Windows 2000 - canned fast
XP - lasted long
Vista - canned fast
7 - probably long lasting
Win 8 is just not fixable. Vista's early problems were performance and application/driver compatabiliy, stuff like this can be fixed. Windows 8 is broken on a whole different level. And since it's Microsoft's policy to never alter the GUI of a Windows version in a Service Pack, Win 8 is doomed and unrepairable.