Well, you see a video on YouTube you really want to have.
But you to have the video too!
In this tutorial, you will meet up with vDownloader (in this tutorial, we use my mothers laptops Vista).

After downloading it from http://www.vdownloader.es, open the ZIP file and choose for the setup.

Just install the shit.

Click vDownloader and your favourite Browser and go to YouTube.

Search for a video and copy/paste the video URL.

And now, give it a location and start downloading!

For some reason, this app is very buggy on most OS's.
In XP it works perfectly, while in Vista, it doesn't download.
And in Linux, it doesn't close.
If you want to use it in Linux, use it through Wine or CrossOver.