Here's a tip for Apple TV owners: Disable interactive booklets. They cause errors with syncing. They appear in your lists without check boxes, but they can actually be disabled by control- or right-clicking on them and choosing "Uncheck selection."
Apple TV thinks these files are movies (because they're in Quicktime format) and tries to sync them to the movies section, but that doesn't work, so deleting or unchecking them is the only way to avoid this issue.
When I was syncing my Apple TV for the first time, I noticed something. With my Airport Extreme Base Station in compatibility signal mode (N/G/B), syncing was insanely slow. About one song per minute and a half. I tried switching the AEBS to N-only, and syncing was about one song per second. That's around 90 times faster. What the hell?
With 3,306 songs, the Apple TV sync would have taken approximately 83 hours to sync in N/G/B mode, but it only took 55 minutes in N-only mode. Something is definitely wrong with this picture.