Fixed gear biking bad for knees?

Hello, I riding a brakeless fixed gear bike on a daily basis. I enjoy it because it is way more aggressive and more fun to ride than a geared bike with brakes. I just worry about the effects on my knees. Fixed gears are supposed to be horrible on your knees, but who REALLY knows??

Here is an article to explain the "danger" from riding fixed gears:

http://yamabushi.wordpress.com/2007/07/03/why-fixies-are-bad-for-your-knees/