Just happen to read this thread.
I did not use the link that Nigel suggested so have no first hand experience but was wondering if you folks are aware of the three FREE programs offered by FREEMAKE, among which freemake video downloader.This allows you to download a YOUTUBE film in different formats, either as an audio or as a video and in different qualities. I can really recommend it to all of you.
I also use their Freemake Audio Converter and Freemake Video Convertor, all with great results.

regards,
John

http://www.freemake.com/nl/downloads/