You don't need an application to download YouTube videos simply - you can just download them via the folks @ google video. Just replace the video ID with the one on your youtube clip:
e.g. to download the number 1 video on Google at the moment ( a Russel Peters comedy clip) , you can enter:
Note that the cache only works for videos uploaded after YouTube was acquired by Google.
Alternatively, you can go to http://keepvid.com/ - which handles many other sites as well.
Thanks again Google! :o)