Apple released iMovie 9.0.9 for Mac on Tuesday. The update improves support for importing projects from iMovie for iOS. It also includes a bug fix and unspecified stability improvements.
Apple's patch notes in full:
What's New in Version 9.0.9
- Addresses issues where iMovie does not recognize video cameras connected to your Mac
- Improves compatibility with projects imported from iMovie for iOS
- Includes stability improvements
You can download the update from Apple's KnowledgeBase entry for the update, but note that it's a 1.08GB download. It's also available through Software Update in the Mac App Store, where it's the same size.