For the motorcycle riders:
I was out for a ride today, and got tired of having to do the zen breathing to keep the fog at bay inside my visor. The weather is overcast and about 38*, which just about guarantees fog even with the shield cracked open a little. I stopped by the local shop and picked up a Pinlock shield with the clear insert.
100% improvement. I literally could not fog the insert, even when I was sitting at a stop light. I have tried various anti-fog stuff in the past, but nothing that even approached the effectiveness of the Pinlock. It cost $90, but it's going to be well worth it for me. I had heard a lot of praise for the setup, but I honestly didn't expect this big of a difference.