I've been noticing that the fan in my Mid-2012 MacBook Air 13-inch has been running almost constantly since I received it -- but I never really paid much attention to it. As it turns out, Apple's uncovered a bug in its new portables that can jack up the CPU cycles to the point where it uses more power than normal.
Apple today released a software update for all the new MacBook Pro and MacBook Air computers (released since June 2012) that fixes an issue "that can lead to increased CPU power consumption." As an added bonus the aptly named MacBook Air and MacBook Pro Update 1.0 (79.7MB) improves compatibility with some USB devices, according to the release notes.
CNet's Topher Kessler notes that the update includes new versions of I/O kernel extensions and frameworks, the Dock application, and some shared resources including desktop pictures, user icons, and system sounds. On the USB front Kessler says that it may also help address problems with USB devices interfering with Wi-Fi signals, or potentially freezing or showing slower performance.
MacBook Air and MacBook Pro Update 1.0 can be downloaded directly from Apple, or via Software Update on qualifying machines.