I used to believe that it should be, at least for private customers, one license per household. Then I realized some households are, well, huge.
I think it may be fairer that Microsoft, for example out of all software, especially OS writing companies, should allow up to two or three installations per CD purchased, like with the Student and Teacher edition of MS Office. I think they did the right thing there.
Consider that a man with a wife and say two kids has to buy the same software FOUR TIMES; when added up after a while, it isn't exactly cheap.
I am literally still smarting over having bought Win XP TWICE because I built each of my kids a computer. Each of those times, I don't recall any discounts or sales or specials. I personally was fortunate enough that another family member, a bit of a computer enthusiast, had an extra real, legal copy that was just gathering dust, so he gave it to me (that guy sometimes has extras of video cards, even hard drives; man!). I was already scanning the onlne vendor sites and various real stores for lowest prices on Win XP. Otherwise, I would have bought it three times.
In those days that way predate Wintel-GUI systems, people lent out their DOS installation disks, antivirus programs (McAfee gave them out free), even Norton Utilities (when it was really great software) would be shared in the same house. And I am from those days, so I suppose my views are colored by them.
Maybe PCs aren't really the way to go:
I should have bought a VAX or something and set up terminals all over my house. At least the kids might learn the meaning of sharing. They definitely won't from today's software purveyors.