Does the 2011 Macbook Air come with a OS reinstall USB drive? Reading through other questions I learned that the 2010 Air came with one, but I don't remember noticing any USB drives when I unboxed my 2011 Air (days ago).
According to Apple.com it does not:

In the Box

MacBook Air
45W MagSafe Power Adapter, AC wall plug, and power cord
Printed and electronic documentation


The air uses Internet Recovery to boot from Apple's servers and then recreate the Recovery HD if needed to re-install Lion (which also will download from the internet). You will only need media if you can't get to an internet connection and have the existing Recovery HD go bad.