Once I upgraded to iLife '11, I began to experience issues loading my Aperture videos in iMovie '11. Also, my Aperture photos weren't available in the Media Browser. It always displayed the message, "Loading Aperture Images." It drove me crazy for a while until I ran across the solution. Now I'll share:

Navigate to your Aperture Library, right click and choose "Show Package Contents." This will open a new Finder window. After you have made a backup of the library file, delete the iLifeShared and the iMovie-Thumnails folders. Reopen iMovie, iDVD or any other iLife product you were having issues with.