James Bannan has discovered that updating the drivers for major system components such as hard drives and graphics cards can cause your Vista system to deactivate and become unusable. Microsoft has confirmed the problem, and it seems there is no way to fix it other than give Microsoft Help and Support a call to reactivate your system.
Windows Vista's activation scheme hasn't changed much since XP. Basically, if you change a certain number of components in your system's hardware configuration, Windows will deactivate as an anti-piracy measure. The problem is, Vista counts driver updates as hardware changes. This can cause your system to deactivate unexpectedly, and without warning.
This is a very serious problem with Windows, especially for mission-critical configurations. If someone unknowingly updates the graphics card drivers to make the system run faster or use a new feature, the whole system could fail. Then the company or individual relies on Microsoft being available on the phone and ready to reactivate quickly. Although the chance of Microsoft's support center being unavailable is small, this does present a serious problem of being "reliant on Microsoft", not just for your initial installation, but for reactivation at any time you feel like upgrading your software.