If you use Ubuntu (or other Linux distribution) and you wish to download some video from youtube.com into .flv file you can try using
youtube-dl command line utility. It just downloads videos without any online applications, converters or etc. Type the following command in terminal to get it installed:
sudo apt-get install youtube-dl
Let’s imagine you would like to download the following video: http://www.youtube.com/watch?v=2leg8mUE9rs (this is part of Military Parade at Red Square in Russia at 9th of May 2010). Just run youtube-dl download utility as follows:
and in a few minutes you will get 2leg8mUE9rs.flv file that could be viewed using almost any video player like my favorite one VLC.