Apple has released Final Cut Express HD 3.5.1.
The update is available for direct download from Apple's website, and also via Mac OS X's Software Update facility. The download weighs in at 14.5MB.
The company has revealed very little pertaining to the update, saying only that "Final Cut Express HD 3.5.1 addresses compatibility on specific hardware."
A note within the latest version of the product manual (Available here in PDF format) states:
"Final Cut Express HD 3.5.1 is a maintenance release that improves performance on Intel-based Macintosh computers."