I had a problem with Ilio-Tibial Band Syndrome (sp?) for a while. couldn't ride more than 30 miles (geared or fixed). Then I started doing the right stretches every day and its all better. I know that ITBS is really an issue that starts at the hip but I think most people think of it as a knee issue b/c thats where it hurts.
Been riding 40 to 70 miles nearly every day and my knees feel great.