No, but like others, I'm not a puker. I had pretty miserable morning sickness during pregnancy, but only threw up once due to some nasty prenatals. I would have liked to vomit if it would have made labor faster!
I just had a pitocin-induced (for PROM), but drug-free labor and birth. I vomited twice at the beginning of transition. I actually preferred vomiting to having contractions, because vomiting doesn't hurt. I would have gladly traded the pain of contractions for vomiting during the rest of my labor.
Not during my first natural birth (with #2)
But once during my second natural birth (#3) which was a 6 hour very intense labor. I guess maybe that was transition? if so it was the only sign of transition.
Oh yeah, lots of times. I don't think I started puking until about the last ten hours of labor though. It was so exhuasting. I remember my midwife trying to pry my vomit bowl out of my fingers to get me a new one. I was scared to part with it for even a second! I puked more during labor than I did my first trimester. It sure does make labor a little less than a beautiful experience. If I got a centimeter for every time I threw up I must have dilated to a 40 before dd came out.