Specifically, the 551KB update fine tunes the speed and operation of the Air's internal fan, which is responsible for cooling the machine and preventing instances of overheating.
The fan, according to several users posting to Apple's support forums (1, 2) over the past two weeks, has failed to perform adequately thus far, resulting in random lockups that render the Air unresponsive for periods of about 10 to 15 seconds at a time, if not longer.
In most cases, the intermittent freezing would occur under CPU intensive operations such as digital video playback, downloading content from iTunes, and the use of resource-intensive applications such as Safari or FireFox.
In these instances, the MacBook Air's internal temperature would rise to abnormal levels, causing one of the system's primary processor cores to power down completely. The weight of the operations would then be shifted to the single remaining core, which would be unable to handle the load, eventually causing the systems to stutter and lock up repeatedly.
"I called Apple Customer Service in Italy, they said they knew about the problem, asked me to run some 'resetting' sequences, but the problem is still there," one Air owner wrote last week. "I really think it is a 'overheating' problem, it only happens when running heavy applications, like video playback or video chatting (skype)."
The issue has been particularly troublesome for Air owners who reside in warmer climates, as the surrounding environmental temperatures serve only to compound the overheating problem.
"Same behaviour here with my MacBook Air running 10.5.2," said another Air owner. "Things seens a bit worst to me because I'm in Brazil, São Paulo. This means 86º F is a ordinary day."
Unfortunately, a couple of owners report that they are unable to apply this week's MacBook Air SMC Update 1.0 because their MacBook Airs shipped out of Apple's manufacturing facilities with the update already applied. These users continue to report freezing issues.
"I download the the update but it told me I was already up to date," one said. "Fingers crossed for a fix soon."
Separately on Tuesday, Apple also released via iTunes iPod shuffle firmware version 1.0.4, which addresses a few bugs and enhances support for the just-release 2G version of the player.