Since Beta 2, Windows Vista has had a fairly versatile and reliable upgrade path from Windows XP to Vista, and in Build 5456, it’s been improved on even more – now you rarely hear of people that couldn’t upgrade, but nevertheless, people suffer as a result of upgrades whether they know it or not.
The most common “symptoms” include patchy Aero performance (if at all), frequent BSODs, drivers refusing to install, and general system unresponsiveness. The problem is that even the experts tend to forget that there is a difference between a clean install and an upgrade, even if everything else worked. When an upgrade is performed, evil things may brew just beneath the surface, waiting for the user to forget that an upgrade is the root of all those problems.
Fortunately there are quite a few steps you can take to protect yourself from buggy upgrades and their corresponding headaches, and they’re not too hard either.