sorry if i'm to late to answer this questions, i think there is only one that powerful enough to download video from youtube, i'm using mozilla firefox and downloadhelper addon, i like this addon because i download video not just from youtube, but from metacafe, dailymotion, redtube, and many more, this add on will download anything on the site that contains flv, avi, mpg, mp3. if you're interested using mozilla and it's addon try my tutorial to do that :
http://helpmyinternet.blogspot.com/2007/07/how -to-download-video-from-youtube.html