I saw that NYT story that Thorn posted, and I'll try to be less of a wuss in the future. BUT, I think the key is keeping it very low intensity, because any time I do a normal intensity workout, it definitely suppresses my immune system. Normally that's good news because it means my allergies go away for the duration of the workout - but when I'm sick, not so much.

Back in my racing days I had a sinus infection that lasted 11 weeks (despite I think four rounds of antibiotics), all because I didn't have the sense to take some rest. I wound up having to take a week not only off the bike, but off work, before I could get better. And when I have a sinus infection, I am sick. Ever since then I've been a total wuss about working out when I'm sick.