Mountain Lion will only be $20 for every computer in the house, and there's a lot of benefits to upgrading to it. Andrew wanted to use iCloud, and that's one big reason, but it's also going to be very secure with Gatekeeper. It'll be worth the wait, but it won't work on all Macs. The older his Macs are, the less likely they'll be supported. He won't have a problem if all of his Macs can't be upgraded though -- they'll all work fine on the same network.