Youtube is one of the most popular video sharing sites on Internet. There are several applications that let you download and store on your hard disk. Elltube is one such application which works both on Linux and windows.
You can download Eltube from here. I installed the deb package for ubuntu on intrrepid with
$ sudo dpkg -i elltube_0.3-1_all.deb
It showed up under Application->internet
The screen shot of eltube is as below.
Now you can download any youtube video by pasting the url of the video to the Elltube window. Locate the video you want to download and copy its URL. On my ubuntu desktop, when I copied the URL, it automatically appeared in ELtube.
You can set the desired location to download the file and specify the out put format. Click on download and enjoy the video.