I was infuriated by the data loss during iPhoto to Aperture migration, but that's nothing compared to iMovie HD to iMovie 11 migration . All titles and effects are lost.
This happened years before the better known debacle; Final Cut Pro X does not import Final Cut Pro 7 projects.
How does Apple get away with this?
It's not just a rhetorical question.
 Prior versions don't import at all, though you can dig the .DV files out of the Packages and import them by hand. Or open prior projects in iMovie HD, then save them then import.