I went on it when I was almost 6 months (and VERY huge) pregnant with #3. I had ridden it before and discussed it prior to our trip with my OB. WDW does say give it a no rating if pregnant. We decided that it would be fine (and I don't have great pregnancies, although this one wasn't too bad unti about 6 1/2 months along).
Yes, it's bumpy, but some roads are bumpier. I don't think it is all that bad. Heck, I've nursed on that ride in the middle and back rows! The CM did automatically put us in the front row.
I'm glad I rode it, but I opted out of additional rides on it that trip. I don't know if I'll ride it again if I'm pregnant on our next trip--probably though. I did skip every other ride that advised against pregnant women riding.