Alternatively, if you use Firefox there's over a dozen Greasemonkey add-ons that add various buttons to youtube videos, including the option of downloading them in high or low quality in a variety of formats, including .flv, .mp4 and .mpg without having to navigate away from the page.
The interesting thing about the .flv files is that they're usually exactly the same as the .mp4 and .mpg files that are harvested in terms of audio and video quality depending on which method you use to pull them. It's quite possible to pull an .flv file from youtube that is of higher quality than an .mp4 or .mpg version of the exact same video. If you pull three versions of the same video using the same method, one of each filetype, they're virtually indistinguishable from one another. If you then convert them to a uniform filetype and do a blind test, you'd swear they were all the exact same file.
