I'm now a staunch fair weather rider.
I was one of those guys who only had a bike. For a little over 10 years. 100,000 miles ridden on Seca 2, VFR and Hayabusa.
I'm making a certain point here about riding in the rain -- riding in the rain in traffic. And this is my bias.
The deal is, when I'm on my bike and it's raining and I'm in traffic, I want to keep a larger distance between me and the car in front of me. Braking capabilities are decreased in the wet, particularly for an average street rider on a motorcycle.
However, trying to keep that extra 1/2-1 second gap between you and the car in front of you simply invites other cars to cut in front of you, hence making the situation even worse.
Riding in the rain on a mostly empty road on a Sunday morning... that's a different story.