@Bri_L For $29 upgrade disc the exact words of the EULA are ” install, use and run one (1) copy of the Apple Software on a single Apple-branded computer as long as that computer has a properly licensed copy of Mac OS X Leopard already installed on it”
Where as for the $169 package the terms are “install, use and run one (1) copy of the Apple Software on a single Apple-branded computer at a time”
The second one may be taken as saying you could use it on 2 computers as long as you don’t use them at the same time. However if you look they include the term install. Even if you are not using both computers at the same time the software is installed on more than one (Apple branded) computer at a time.
While I think everyone should be able to make their own mid up on this, I personally would pay the extra $20. A lot of the time software is ridiculously expensive (just look at MS and windows 7, for example) Apple has been quite reasonable over the price and I think it would be a good idea to encourage them to keep doing that.