For those who dont use Firefox, theres a handy program called "Free Studio" by DVDVideoSoft that lets you download videos to your computer, or save the audio from youtube vids as mp3's so you can listen on your mp3 player or burn to CDs, as well as converts video formats, etc.. its completely free with no adware or anything at
http://dvdvideosoft.com/free-dvd-video-software.htm