GNU/Linux users:
1. Install Greasemonkey and 'Youtube - NoFlash-Player' script from userscripts.org
2. Get rid of any Firefox media player plugins.
3. Install gecko-mediaplayer instead (based on mplayer, it's in the sudo apt-get install repos in Ubuntu)
4. Enjoy 100% more performance for YouTube videos and direct download links right under the videos.
5. Have a nice day.
6. Profit!
(Windows users can just grab the 'Windows Media Player V5' script instead, instructions would be similar I guess...)
Destroy flash!