I have a rule with ANY product, no matter who the manufacturer is. Simple - three strikes and you're OUT. If you have three defective units, what does that say about the manufacturer? I don't care if it's Microsoft, Apple, Samsung, whatever - three bad units and enough is enough. That's my opinion.
Knock on wood - so far, I haven't had problems with defective SP3s. I'm still on my original unit from June 20th, and other than the wifi/sleep problems that almost everyone has, the thing works. I did have a defective SP2, and the MS Retail Store swiped it out no questions asked.