How to install OS X Lion on all the Macs in your house for $29.99
The Apple OS X Lion update is a huge file, about 4GB of data that took me over two hours to download on fast connections. You can install it on all the eligible Macs in your house for $29.99, and if you don't want to download it several times to do the installs, follow these instructions.
Go to the App Store and download it from one Mac linked to your iTunes account. When the download begins a Lion's head will jump from the App Store to your Dock and it will say it's installing. When the download is complete the Lion icon in the Dock will change to an arrow and it will say "Install OS X Lion." AT THIS POINT DO NOT RUN THE INSTALLER. If the installer has launched, quit it and also quit the App Store. If you run the installer on the first machine the installer file will be deleted and you will have to download it again.
Now look in your Applications folder for the installer file, called "Install Mac OS X Lion." Copy this file to a hard drive or USB key chain drive, or burn it to a DVD. You can then use the installer file to install the update on all the Macs in your house, including the one used to download it.