Don't forget that a cross training is a crucial part of staying in shape! Use that day and go for a run. Or if you don't run (ie. don't have running shoes), go to gym in the morning, do some elliptical and weights and then again in the evening.

I generally ride in rain but only if it is light and without traffic. My opinion is that it is always better to have one day less training than broken collar bone.

That said, I am in the same boat. I am doing the MS bike ride 100 miles next weekend on my FIXED gear bike and this weekend suppose to be my last big ride. And it is pouring and pouring and pouring. I will wait and see how the weather looks tomorrow.

If you decide that you ride tomorrow, slightly underinflate your tires - you get better traction on the wet surface and be easy on brakes on downhills. Generally, in wet conditions you should ride a bit slower and very careful in high speeds.

Good luck and let us know how the weekend unraveled for you,

Martina