If you have the URL, like http://www.youtube.com/watch?v=5i4xgDYl1Lg .... Then, stick its ID number (5i4xgDYl1Lg) with at the end of this URL like this: http://cache.googlevideo.com/get_video? to become http://cache.googlevideo.com/get_video?video_id=5i4xgDYl1Lg ... It will become a downloadable FLV file.

Who how long this trick will work... Thanks to James Thomson, from Funny Animal Videos, for this tip.