Today Apple offered up an update to fix hard drive problems that some Mac users were reporting. The Performance Updates for both Leopard and Snow Leopard are supposed to, "[Address] intermittent hard drive-related stalls reported by a small number of customers." 

A few Mac users were experiencing these hard drive-related problems, and these problems have been reported for a while now.

You can download this update by visiting the Apple Support Downloads page for Leopard (Mac OS X 10.5) or Snow Leopard (Mac OS X 10.6), or you can open Software Update (Apple menu > Software Update). Apple has also created a page detailing the steps needed for installing this update.

Not all Macs need this update. The Macs affected are:

MacBook Air (Mid 2009), MacBook Pro (17-inch, Mid 2009), MacBook Pro (13-inch, Mid 2009), MacBook Pro (15-inch, Mid 2009), MacBook Pro (15-inch, 2.53GHz, Mid 2009), iMac (20-inch, Mid 2009), MacBook Pro (17-inch, Early 2009), MacBook (13-inch, Early 2009), MacBook (13-inch, Mid 2009), MacBook (13-inch, Aluminum, Late 2008), MacBook Air (Late 2008), MacBook Pro (15-inch, Late 2008), iMac (24-inch, Early 2009), iMac (20-inch, Early 2009), Mac mini (Early 2009)