The issue seems to affect only those users who own the current model -- officially called "late 2010" MacBook Airs -- and have upgraded to 10.6.7 (and are running iTunes 10.2.1, the current version).

After a number of reports, two possible "fixes" have emerged. The first one, which seems to work for most owners, is the simplest: after the freeze and a forced shutdown has occurred, restart the MacBook Air normally but do not launch iTunes, then shut down the machine normally and restart. This second, manual shutdown seems to have fixed the problem for a number of users.

A second method in case the first one doesn't work involves locating and deleting the file "iTunes Library Genius.itdb," which is located in a user's home folder inside the iTunes folder, which is itself inside the Music folder (or ~/Music/iTunes). The user then launches iTunes but immediately quits it, and then launches again closing the sidebar. The action forces the Genius function to rebuild its database, which appears to resolve the issue.