As pointed out by forum member Spider, Apple has released iMovie 5.0.1, an update to iMovie HD, which is part of the just-released iLife i05 suite. The update notes say simply, "iMovie HD 5.0.1 addresses issues related to video and audio synchronization for DV projects and other minor issues."
The update can be downloaded through Software Update if you have iLife i05 installed, or downloaded through VersionTracker. You can find more information on iLife at Appleis Web site, where it is priced at US$79. Amazon is currently offering it for $73.99.