FeynTube achieves this accomplishment by doing the only conceivable thing: removing all YouTube comments (from your display, unfortunately they're still on the servers) and replacing them with actual quotes from famous nobel-price physicist and elaborate skirt chaser Richard Feynman.
I wrote it because I actually like watching videos on YouTube, but, despite better knowledge, sometimes just couldn't restrain myself from scrolling down and reading some of the comments--with horrible consequences. So I wrote this small script. Now, everytime I scroll down to the comment section, I can read something worthwile.
Once you have Greasemonkey installed, just click: feyntube.user.js. Greasemonkey should ask you if you'd like it to install the script. Answer yes. That's it, you're all ready.
(Hint: disabling Greasemonkey, temporarily or permanently, including FeynTube, is very easy: just one click on the monkey head on your browser status bar. However, read YouTube comments on your own risk.)
Next step: Visit YouTube and enjoy. However, keep in mind that FeynTube only modifies YouTube pages and nothing else. With Digg, you're on your own.
Update 2008-05-22: FeynTube was broken after YouTube's redesign. Dan Phiffer fixed it and now it works again.