to commonly asked questions.

Saving YouTube Videos to your HD.

What’s an easy way to rip videos off of youtube?

While I won’t go into the legal questions of doing this, try one of these sites:

Just enter the web address of the youtube video and the website should do the rest.

You could also enable Developer Mode in Safari and use the activity viewer to see the video file cached then pull it that way as well but the aforementioned method is easier.
This image is a theme.plist hack