I faced this problem once when i was first shooting swimming and water polo at my college. I got a tip that you can actually put your lens and body in plastic baggies like a zip-lock, and the condensation on the camera and lens will try to evaporate but it will just form up on the inside of the baggies. Then you can take your stuff out and shot away. I dont know the exact science behind it but i've tried it and it works pretty well.
I guess that I am the only one who has used an anti-fog product on my lenses. Since Nikon puts its name on anti-fog sheets, I figured that they could not be very damaging to a lens. By the way, they work great. I have used them several times, with no noticable ill effects. I have used an anti-fog sheet on my lens and viewfinder, immediately before going from cool, outside temperatures into a hot, humid butterfly pavilion, and was able to start shooting immediately. Without the anti-fog treatment, it takes at least 15 minutes in the pavilion, before shooting is possible.