I'll say that M$ will just kill people with WinXP in 2010, a.k.a (Windows XP is no longer supported and developers are to make it compatible with the newer versions).
I use Vista [OEM] and I got like 10 errors each day, from CONFIG.NT, ActiveX, missing .NET component. I think Vista is doing sth like this:
If you install driver.dll, delete driver.dll
If you reinstall CONFIG.NT, delete CONFIG.NT by 3 days
If you install an old program, return "Runtime Error", "16-Bit MS-DOS Error"
Buying Vista would be cool only in Mar 2008, last time during WinXP launch, I bought it 8 months after the launch (in my country).
P.S. Vista is not based on Longhorn, which is based on XP (e.g. Vista's boot system is different from XP's boot system and that is why you cannot dual boot to XP because Vista will not load once you install XP).
P.P.S. That is why Vista came late, it should come in early 2006, they throw the Longhorn code away after like 1 year in development.