I had a frustrating experience with iPhoto 9.2.1 under Mac OS X 10.6.8. iPhoto got into a state where it would beach ball shortly after launching regardless of the state of the OS (fresh boot, fresh image, etc.). Turns out the problem involved movies from a Canon SD870 IS camera. Here’s what to do if this problem befalls you.

1. In the Finder, move the photos off the memory stick and into the movies directory. Delete the *.thm files.
2. Force Quit iPhoto
3. In your ~\Library directory search for iPhoto in the “Library” directory (not “This Mac”) in the “Filename” (not the “Contents”). Delete iPhoto from the caches directory and the 1 or 2 plist files in the Preferences directory.
4. Empty the trash
5. Reboot. The reboot is important. Something remains in memory otherwise, it’s not clear what. You can tell the difference by what happens when you launch iPhoto after step 3. If you don’t see iPhoto first-run activity (welcome to iPhoto) then you know something didn’t get removed. I consistently saw first-run activity after a reboot.