New
#11
Well, the 3-day activation limit is true as far back as XP. I did an old XP x64 OEM image restore over a different MB and after clicking on the gazillion New Hardware Found pop-ups, I got the "WTF??? The hardware has changed significantly, you have 3 days to activate."
I didn't pursue it any further as it was just an experiment.
I should also add that as Sevman mentions, I've never had a problem getting re-activated after a phone call if it sounded reasonable. I don't think they're so much worried about some poor bloke upgrading his system, more about somebody cranking out an assembly line with only one license.