Hmmm tell that to your support staff in India.

I've always used OEM versions (up till now as I bought the cheap pre-orders this time) and always shifted them around. When I've needed to call into MS to get the activation limit reset, the nice lady in India just asks me to make sure its only installed on the one PC (which it is) and away we go.

I dont think MS really cares, after all they got your money, they just put the odd scare warning out to try to make a bit more.