I expect I'll get flamed for saying this, but only an idiot would bike in rain.
When on a bike in wet weather braking capability is but a small fraction of what normal braking is. That's reason enough not to do it.
Maybe if you live in a very rural area and never have to brake at all you can get away with it. I live in a citified area with cars, pedestrians, potholes, and a high population density of idiots, all of which might require accident avoidance vigilance (read: braking).
IMHO biking in the rain increases risk of accident and personal injury substantially. It just isn't worth it.
Unless you want to be a candidate for the Darwin Awards...
