I recommend carrying a lightweight point and shoot that is relatively inexpensive. My rationale is that it is fun to keep the camera tucked in your jersey pocket where you can reach around and grab it while riding and take a shot while in motion. On my TransAm we all began doing that and were able to get some great shots on a spur of the moment basis. Try that with a D70 (which I have and love...just not for a bike tour).

I also managed to drop my camera while riding and while the camera survived, again, try that with a D70.