I've experienced this too many times to count. It feels amazing, fucking a woman as a guy fucks my ass, it results in the strongest orgasms! I urge everyone to try this at least once in your life.
We've tried this a couple of times - it takes a bit of setting up but my wife loves the feeling of being fucked by two thick cocks at the same time. Also, i can feel the other mans cock through my wife's vaginal wall.