A nice option that now comes tucked away inincluded documentation is a USB key containing a full version of the Mac system software and .
When plugged into the computer, holding down the "C" key as you boot up treats the USB stick just like an optical disc, letting you run system diagnostics, or do a clean re-installation of OS X. Apple has long included the same tools on CDs, and later DVDs, but given the Air's reliance on external disc drives, this proves to be a much more user-friendly option for those without.
Is this pack-in a sign of things to come from the hardware and software maker? It very well could be a future option of bringing upgrades, like the upcoming 10.7 Lion to the Air when it arrives next summer. Either that, or through the, which Apple said will be coming to computers running Snow Leopard (10.6) in the next 90 days.