B. Mac App Store License. If you obtained a license for the Apple Software from the Mac App Store, then subject to the terms and conditions of this License and as permitted by the Mac App Store Usage Rules set forth in the App Store Terms and Conditions (http://www.apple.com/legal/itunes/ww/)
(“Usage Rules”), you are granted a limited, non-transferable, non-exclusive license:
(i) to download, install, use and run for personal, non-commercial use, one (1) copy of the Apple Software directly on each Apple-branded computer running OS X Lion or OS X Snow Leopard (“Mac Computer”) that you own or control;
Regarding the legality of whether you "have to buy a second copy":
Official OS X 10.8 license:
http://images.apple.com/legal/sla/docs/OSX108.pdf
Specifically:
That's interesting....Reading the fine print pays off....I was always under the impression that there was a 5 Mac limit for some reason....The "You Control" part is also interesting as well...implies that if you were an IT pro and "Had Control" of a dozen or so Macs you could use your ID to install ML on all of them. I have three Macs, and obviously paid once to install ML on them all. Practically a giveaway at £13.99 in the UK too.
(ii) If you are a commercial enterprise or educational institution, to download, install, use and run one (1) copy of the Apple Software for use either: (a) by a single individual on each of the Mac Computer(s) that you own or control, or (b) by multiple individuals on a single shared Mac Computer that you own or control. For example, a single employee may use the Apple Software on both the employee’s desktop Mac Computer and laptop Mac Computer, or multiple students may serially use the Apple Software on a single Mac Computer located at a resource center or library;
C. Volume or Maintenance License. If you obtained the Apple Software under a volume or maintenance license program with Apple, the terms of your volume or maintenance license will determine the number of copies of the Apple Software you are permitted to download, install, use and run on Apple-branded computers you own or control. Except as agreed to in writing by Apple, all other terms and conditions of this License shall apply to your use of the Apple Software obtained under a volume or maintenance license.