I read that Apple would allow you to use Lion as a virtual machine. However, if you don't get an install disk with the new MBA, how can you install Lion as a virtual machine?
Actually, download it, then move it from the apps folder to another location as it deletes itself after installing on that machine.
Also, some developers might want a clean instal to test apps and not have to worry about hosing their own workspaces.
It depends on your requirements. You might not need to run OS X in a virtual environment. But as a software developer or sysadmin, that sort of thing is invaluable for testing purposes. I'm happy to see that Apple's OS X license now allows such things - it's going to make my job easier.