After weeks of gruelling troubleshooting, I've finally had it confirmed by Microsoft Australia and USA -- something as small as swapping the video card or updating a device driver can trigger a total Vista deactivation.
Put simply, your copy of Windows will stop working with very little notice (three days) and your PC will go into "reduced functionality" mode, where you can't do anything but use the web browser for half an hour.
You'll then need to reapply to Microsoft to get a new activation code.
When the machine is first activated, Windows establishes a baseline based on the installed hardware, but interestingly the information is not gathered from hardware IDs (which are not necessarily unique), but from hardware information as reported by device drivers. Any changes away from this baseline are weighted depending on the change (for example, a new CPU counts much higher than new RAM) and once the baseline threshold is passed, Windows deactivates and a new activation request is generated.
The problem with using device drivers as the basis for activation information is that a change in the driver model which has the result of changing the way that the hardware information is reported back to Windows can be enough to register as a physical hardware change.
For example, if you install and activate Vista using some Microsoft drivers downloaded from Windows Update (which is a very common practice) but then discover that a manufacturer driver gives better functionality (as is often the case for audio, video, storage and network drivers) you are running the risk that the drivers use different reporting models and will register as a physical change.
So what this essentially means is that keeping your drivers up-to-date is a potentially very risky process, with all changes monitored and changes weighted cumulatively.
Yes, I know what the guy's talking about; I have had that happen to my Apple O... Oh, no, no I haven't, because Apple OS distributions don't have a serial number and you don't have to activate them: they just rely on people being honest. Aaaaahahahahaha!
Seriously, how can you Windows people live with the very idea that your entire system can be shut down, simply because you have been keeping your essential software up to date, whilst Microsoft arses around attempting to get a new activation code to you?
For fuck's sake, the things that people will put up with are just extraordinary...
Windows is one of those things: this fucking government is another. In fact, that's it! This NuLabour government is the Windows of politics. Now, if we can just find a way to deactivate the fucks, not bother phoning Microsoft and then switch to Apple...
DISCLAIMER: I own Apple shares.