I have 2 macbooks (the unibody and the one before that). Do I need to buy two licenses or can I just use one license for both machines?
Like everything else you purchase in the Mac App Store, you can install Lion on all of your Macs after buying it once. There is no activation process or DRM.
Here's the relevant excerpt from Lion's license agreement (emphasis mine):
If you obtained a license for the Apple Software from the Mac App Store, then subject to the terms and conditions of this License and as permitted by the Mac App Store Usage Rules set forth in the App Store Terms and Conditions (http://www.apple.com/legal/itunes/ww/) ("Usage Rules"), you are granted a limited, non-transferable, non-exclusive license:
(i) to download, install, use and run for personal, non-commercial use, one (1) copy of the Apple Software directly on each Apple-branded computer running Mac OS X Snow Leopard or Mac OS X Snow Leopard Server ("Mac Computer") that you own or control;
Technically you can use the Lion installer app from the app store to all your mac. Don't forget to move the installer from Applications folder before install Lion. it will deleted if you won't move the installer after the installation process.
Another good alternative is to create bootable DVD installer for Lion. You can use it to install Lion for all your mac. Follow this step to create it
Anyway i have tried both from installer app and bootable DVD installer to install Lion for several mac. It works well.
You have to have your employer buy a license.
Your personal license can be used to install Lion on every Mac you own or control for personal, non-comercial, use. So it can't be used to install Lion on your computer at work. Your employer can buy a license and use it to install Lion on each of the Macs it owns or controls, as the following statement says:
If you obtained a license for the Apple Software from the Mac App Store [...] you are granted a limited, non-transferable, non-exclusive license [...] (if you are a commercial enterprise or educational institution) to download, install, use and run one copy of the Apple Software for use [...] by a single individual on each of the Mac Computers that you own or control