I just read on omgubuntu that is now possible to install an Unity Lens that makes you able to search in the youtube directory and play videos direcly using VLC if installed.

This is the original article: http://www.omgubuntu.co.uk/2012/01/unity-youtube-lens-updates-with-browser-free-video-playback/

Setting it up is very easy, just run the following commands:

sudo add-apt-repository ppa:atareao/lenses

sudo apt-get update && sudo apt-get install lens-video scope-youtube

Happy watching!