I bought a new iMac and the newly released MBA so now I'm downloading free Lion on the iMac. Can I put it on a USB stick and then instal it on the MBA after installing it on the iMac?
Yes. Make the USB key as described in the above post.
Then plug the USB key into the MBA. Restart and hold the alt key when starting. Then select the USB key to start from. From there you will get a "install Lion" screen. Works perfectly.
You don't even need to put it on a USB drive. I just copied the Install Lion app in the Applications folder over to the other computers needing the upgrade, then I ran that app/installer from there.
Yes, so you need to copy it over after it is downloaded, but before it is installed. I threw the entire installer file onto an external hard drive after it downloaded. For each of my computers, I just dump it into the Applications folder on the computers in question and launch.