Yes, I was lucky enough to ride Nemesis at Alton Towers in the Rain.
Basiclly, I had queued up as normal, and decided to queue for the front, anyway, me and my friend were the next people on when it decided to rain(and it really rained hard too) We expected them to stop the ride, but were shocked, when the ride kept on going(Nice one Alton;) the experience was totally worth it, It was running Twice as fast and we got such a WILD RIDE. I may have got soaked and it hurt like hell, but it was so so worth it :)