Hey Dave,
I had this issue only once before but was lucky enought to find it was a specific event causing the import to freeze. It took me some time to isolate the problem though. I would recommend letting it sit there for some time before you try any troubleshooting. Larger libraries can take long periods of time to update.
This is a good thread for this issue. I would first try removing the iMovie.plist as elikness mentions.
1. Open Finder
2. Click on "Go" in the menu bar.
3. Click on Go To Folder on the dropdown menu.
4. Type "~/Library/Preferences/" in the text field and click Go.
5. Find the com.apple.iMovie(some number).plist file and move it to Trash.
Quit and relaunch iMovie to see if this took care of the issue before attempting the next step. If you're still having an issue then you can try what I needed to do which is isolating the problem event.
1. Open Finder.
2. Go to the Movies folder. You should see iMovie Events here.
If you have a larger event library I'd recommend renaming the iMovie Events folder to say, "iMovie Events COPY". Then create a new empty folder named “iMovie Events”. When you launch iMovie 9.0.9 all events will be missing at this point. Quit iMovie if it is open. Then you can either drag each event from iMovie Events COPY to iMovie Events or you can select and drag several at a time. Each time you drag an event folder back into the new iMovie Events folder launch iMovie 9.0.9 to see if you are having the same issue. Wash and repeat until either you have found the problem event or you have imported all events.
If you find the problem event you can reimport the clip from iMovie 9.0.9 by going to File > Import > Movies and navigating to that events iMovie Original Movies folder to find the clip.
Hope this helps!