My first commute in the rain was when I picked up my brand-new bike last year and rode it home. I didn't have anything, and I arrived soaked and with an ear-to-ear grin.
Today I did my first "real" commute in the rain - ran some errands downtown, and then went to another bike shop to buy a front light - I already had a pretty decent rear one, but no front light at all.
So I buy the light, and it starts POURING. It was getting close to sundown, and although I now have lights and was wearing a reflective vest, I didn't really want to wait until it was pitch dark to see if the rain subsided. So I started the ride back home.
Lessons learned:
- Fenders work. But past certain speed, I need mudflaps! I have some leather at home; may as well put it to good use.
- Now I see why you people keep going on and on about leg/shoe coverings

Need to get some if I intend to ride in the afternoons this spring - that's when it rains here. Opinions on coverings vs. ponchos/capes/whatever?
- Lights are awesome. Pedestrians see you! Cars see you pass them, soaked and happy!
- Why did I leave the non-slip gloves at home. Brake hoods and levers get uncomfortably slippery with rain.
- I use toe straps and regular shoes - it was harder than usual to get clipped, as the pedal would slip a bit when doing the kick-it-back-to-get-clipped dance.
- Rain is nicely refreshing.
I guess I should wash the bike tomorrow...