DISCLAIMER: I am not encouraging anybody to download videos! If I gave you that impression, then I think my English sucks. Do so if you want to! (After considering all the legal and ethical hassles!!!!)
I got this little trick from a website that I was browsing. It’s pretty neat:
First install FireFox if u don’t have it already.
Next : Download a plug-in called “VideoDownloader™” from firefox addons.
Go to Youtube -> get to the movie page (that is, where the movie is playing in the flash player)
Stop the flash player.and click on the little button on the right hand corner of the screen. The icon is shaped like two windows.
OR:
Now wait for it to generate the link : it takes 2 seconds.
Next, right click on the link, and click on SAVE AS. (be sure to save the file as (filename).flvNow you will have a flv file.
To play it, you need FLV player. Download it for Free from here .
if u need to convert it to some other format, use IMTOO encoder. This can be downloded for free, or can be registered.
That’s it enjoy! 
