Alot of people may know this others might not.
So i'm sharing it with those who might not!
Info:
This Tip will show you how to download a program named Real Player, with the latest version of Real Player installed it allows you to download videos you watch online.
Go to Free RealPlayer - Download Online Videos
Press this:
Download and Install it all.
Once all thats done go watch a video and this little icon should pop up when you mouse over.
Press it, and a window will pop up with the download.
Once the download is complete simply open and enjoy.
WORKS FOR MORE THAN JUST YOUTUBE!