I've ridden in the rain with no problems. I'm most careful when the rain just starts to fall, as there may be oils on the road that mix with the rain and make it slick. But I've never had a problem with having the tires slide around on me; maybe I'm just too slow .

It's interesting to hear about rain tires for bikes, I guess I've always believed Sheldon Brown when he says that bicycles don't hydroplane and bicycle treads (road bikes) really provide no benefit. I'm not saying one article defines all truth, but it makes sense to me. If you haven't seen it, here's a link: Sheldon Brown on Tire Treads