I too labored in the tub but didn't actually birth in it. When the baby was crowning, the midwife said, "we better get you to the tub quick or the baby will be born right here on the bed", and I said "and.....?" (as if I couold walk with the head hanging out like that). I had a difficult, long labor and I don't know if I could have done it without the tub. It made a WORLD of difference; I can't even express how much. My midwife kept making me get out to walk around and I REALLY didn't want to.
I'm also a doula and Bradley teacher, so I've attended quite a few births, and if you're planning a natural birth, ABSOLUTELY do it out of the hospital if you can-it's soooooo much easier; no arguing, no machines, no positions you don't like, no being confined to the bed, no one there who doesn't have the same ideas you do about what you want your birth to be like, no 25% c-section rate.
Just my humble opinion.