I try not to ride over them or using the brakes if I have to ride over them.
Most of them here in Calif. are painted on and they get worn pretty fast so they don't stay slippery for long.
The only time I had a problem with wet road paint is when I was running Metzeler tires. Then again, everything was a problem in the wet with those tires.
Put some Avon or Pirelli tires on and you will not have to worry about it so much.
Man hole covers act the same way. The man hole covers in the road, not the one's girls I meet wear. They act like they are wearing chastity belts and they are anything but slick or slippery.
I rode over a manhole cover one time while it was wet out and at the same time accelerating pretty hard. That was probably the fastest I've seen the rpms shoot up and the last time I went over a manhole cover.