I've had the unpleasent experience of within 1 week having my mother board replaced twice, and my wireless chip and keyboard replaced once. (And my bios service tag not properly reset after one of the motherboards). Through all of this, Windows somehow got the idea that I was pirating it (okay, pretty clear where it got this idea from). The license key that came with the CD did not work. After several boot cycles and re-tries at activating windows, I decided to try again, and when it failed that time I would use the activate by phone option. Somehow, when I ran the activation executable that time it activated without any further prompts. Not entirely sure what this story says about MS's computer fingerprinting.

Also, I left out of the story that: After the last hardware change windows booted several times without issue. After the first time it complained it was invalid the computer would fail to boot until I re-installed GRUB from a live cd. Between the GRUB incident and windows activating I identically let windows install updates (which I thought couldn't be done from an unactivated install). After these updates, when you try to log on, you get a fatal error in its attempt to launch 'your copy of windows might not be genuine' program, followed by a failure to launch explorer, followed by a black screen. I looked up the error, and it seems to be a result of the update unrelated to the activation issue. Booting into safemode and installing the update solved that. Several failed activation attempts later and my computer was good as new.)

One of the many reasons I use GNU/Linux as my primary OS.