Many utilities for downloading YouTube videos use the iPod-friendly MP4 format, but even after adding the files to your iTunes library, that won’t make them synch to a connected iPod. What gives?
It’s doubtless deadly obvious to those who’ve already done it, but if you’ve encountered the problem, it’s worth trying iTunes’ built-in converter. Add the video to iTunes, select it, and then choose Advanced –> Create iPhone or iPod version, and let iTunes do its converting thing. The downside is you end up with a duplicate of the file, but you can easily delete that.
For automated solutions to iPod video downloads, check out previously reviewed iPodME and MXTube. To save on wasting space when converting DVD files for use on your iPod, consider ditching H.264 for conversions.