Spotted this over at Bit-Tech earlier today:
"A Microsoft spokesman... told us that Windows Vista will not require a system re-activation unless the hard drive and one other component is changed. This means that enthusiasts will be able to swap CPUs, memory and graphics cards out without any worry about having to re-activate with MS, either on the internet or by phone.
Should you change the hard drive and another piece of hardware - for example for a major upgrade such as a motherboard change that requires a re-installation - Microsoft will allow you to re-activate up to 10 times. You will not, however, be able to have more than one machine activated concurrently."
This could pose some serious problems for enthusiasts that are constantly switching rigs or components around. Although Microsoft reserves the right to allow more than 10 activations per copy, the bit-tech folks believe keeping a base 'activated' image of Vista might save some headaches down the road.
Update: Yes, the article is rather vague but does raise some interesting issues. Most importantly, what does Microsoft consider a re-activation to be? According to the article you wont have to 're-activate' a copy of Vista unless you change the hard drive and an additional component. If I simply reformat my existing Vista PC and run the activation wizard, will I have used up one of my ten activations?