A well maintained registry very seldom causes problems. The one office I spend a fair amount of time in has about 28 windows XP boxes and 2 windows servers - In the last 5 years I've reistalled windows only ONCE except for when a motherboard was changed and the new board wouldn't boot off the old drive because of a video driver issue. ( and this happend 2 or 3 times)
If software developers follow Microsoft's well published rules about drivers and DLL files, everything works just fine. When they don't, a utility like CleanMyPC from registry-cleaner.net sorts things out pretty well in a very short time.