Dwight Silverman at the Houston Chronicle writes about how he had to call Microsoft and reactivate his copy of Vista because he made too many hardware changes to the machine it was running on. The twist is that it was a virtual machine (he's running Vista virtually on a Mac) and one of the benefits of virtualization is that you can change the "hardware" configuration of machine at will. (Got a memory intensive task? Bump up the memory. When done, reduce it again. Etc.)
This of course trips up Vista, which decides that the machine has been tinkered with too many times and thus is not really the same machine on which it was installed... so it stops working properly until you call Microsoft to explain that you are a real customer, not a thief.
I'm surprised people accept this so meekly (check out the comments to Dwight's post). Products that stop working when you buy them and use them legally are not well-designed products. It's a bit like having a car that periodically stops running unless you scan a copy of your title documents into it.
I understand Microsoft's wish to reduce piracy of its products; that's perfectly legitimate. But isn't there a better way than treating your customers like thieves, making them prove that they did not steal the product?