The latest MacBook Air, which I have, has developed problems with iTunes making the Mac freeze up after the 10.6.7 update. My update went fine for a few days, but then I also developed the problem.
Fortunately, Apple is on top of this, with a supplemental update.
I am about to install this but it will take a few days to know if it worked as promised. Posters to Macintouch have stated that it fixed their problem.
This affects ONLY Air users running 10.6.7. No word of problems with the newest generation of MacBook Pro models.