no es video pero es útil...
Instrucciones para bajar los videos de youtube.
Firefox (Windows only)
1. Add the Greasemonkey extension to your Firefox browser.
2. Go to http://www.userscripts.org and install the Download YouTube Video script.
3. The next time you watch YouTube, you?ll see a Download Video option beneath the screen. Click it to save the file to your desktop as QaQw9V4Upj4.flv or whatever.
4. Install and launch the free Super video converter (www.erightsoft.com).
5. Select Apple ? iPod from the Output Container option, and then the output video codec H.264/AVC. Set size to 320 x 240. If you get an error message when converting, unclick the Use DirectShow button. Otherwise, drag the converted file into iTunes and it?s ready for viewing. (sólo si tienen ipod, sino seleccionen .wmv o algún otro que les funcione)
{fuente:wired magazine}