One of the upsides of OS X Mountain Lion's already low purchase price of $20 is that one copy can be re-downloaded and installed on any other Macs that you own for free. The downside, of course, is that if another Mac in the household doesn't share the same Apple ID as you, the buyer, you have to get another copy. As it turns out, there's a very simple solution so you can just reinstall from the same copy as many times as you need to. More »