Yes it's harder to brake in the rain...the rim is slippery so the pads don't grab well at first, then they may suddenly grab too tightly, and the road is slippery so the wheel may lock and drift. Especially avoid braking over road paint or metal grates (or taking a banked turn over them) because they are even more slippery than the pavement.

Good advice, Cooker: avoid metal set into the road. Also, watch for painted lines! They can be like ice.

My bicycle has no rim brakes at all. Both are drums, so there's no brake pads to change or whaver.

Yes I have steel rims. I chose the rims specifically because I don't consider aluminum an "upgrade" in terms of looks and long-term durability. And I chose the drum brake hubs specifically to go with said rims.

Riding drums is really incredible. I've had bikes with canti brakes on textured aluminum rims and the braking quality is good in poor weather, but still nothing like a fully enclosed brake system. The brakes literally don't even notice weather conditions. You have 100% of dry stopping power no matter what. Also the brakes' power application is much more gradual than canti brakes (more like calipers) meaning that you have a lot of control over how much force is applied. There's less chance of accidently skidding a wheel.

First off, my braking systems are kept very good care of, and are chosen specifically for their wet weather performance, even if it's at the cost of dry weather performance.

My tire choices are also based on wet performance, as is my lights.

I immediately pull into a sheltered area, and put on my raingear. Then i get back on the bike, throw all lights on blinker mode, and trudge on.

Remember that you will probably have to remove your shoes to put on the rainpants...so it's a wise idea to have a plastic bag to put one foot in wihle you are doing this. I keep one in my bag.

Also never commute without your rain gear, ever. This prevents forgetting it the day it might rain.

edit: oh and disc brakes may be noisy in the wet, but you cannot even come remotely close to the reliable stopping power of a good disc setup.