I helped a customer today who had a MacBook Air that was no longer booting due to a logical issue (corrupted directory) with their internal HD Main Boot drive. She did not have her data backed up, so she wanted to use Data Rescue 3 Mac Recovery Software to recover the files from the drive before she attempted to reinstall Mac OS X. Since her MacBook Air was not booting from the Main HD hard drive this was tricky because there is no optical drive to use the Data Rescue 3 Emergency Boot DVD and the MacBook Air had no FireWire port that you could use for Target Disk Mode.
I helped guide her to boot into the Lion Recovery partition and she was able to Install Mac OS X to an external USB drive. Once the install was complete, she was able to boot from the external hard drive, I helped her download and install Data Rescue 3 to that newly created bootable hard drive. Once she had done that, she was able to use that drive to boot up her MacBook Air, run Data Rescue 3 from it, and scan the main HD internal boot drive on her MacBook Air. When Data Rescue 3 was done scanning her internal drive, she was able to copy the files from that drive over to that newly-created USB external drive.