Camprax, I think you're mistaken there. From the You Tube help page:
Can I download videos to watch later?
No, currently you can't download our videos to your computer. YouTube's video player is designed to be used within your browser as an Internet experience. As an alternative to downloading, you can temporarily save videos to watch later by adding them to your QuickList. If you'd like to save them more permanently, login and click "Save to Favorites" under the videos you'd like to keep.