I've never tried castor oil, but I have been induced. Honestly, it was a great experience. It all depends on your frame of mind going into it. If you're nervous and stressed, it doesn't help. But I was fresh from a full night of sleep, and relaxed, and from start to finish, it took 6.5 hours. I was up and about as soon as they finished all the tests and stuff they do when the baby is born.
I have herd the nipple stimulation will help