Apple has released MacBook Air (Late 2010) Software Update 2.0 for the latest MacBook Airs. It’s a 342KB download and requires Mac OS X 10.6.5 or higher.
According to Apple, this update resolves an issue with some MacBook Air (Late 2010) systems that prevents the system from sleeping. You can obtain the update via the Software Updates component of Mac OS X’s Systems Preferences app.