Kim - When i had tori i spent most of the labour on my fitball at home and then at the hospital again on the ball but in the shower and i ended up with her popping out while i was climbing up onto the bed to get on all 4s.
With charlotte though, as you know i was induced and had to be monitored which was terrible and they doubted that what i was feeling was real contractions untill they started reading the print outs from the monitor. I managed to at some stage of it convince one of the midwives to let me off the machine so i could go for a walk for a while (we agreed on 15mins) and that was great and obviously when i managed to get most of 2nd stage over with. Almost as soon as i got back to the room i asked to be taken to the birthing suit (they still didnt believe i was ready though) when i got around to the birthing suit i was hooked up again but this time i had a lovely midwife who let me move as much as i wanted and she just followed me around adjusting the monitor and even holding it on for a while there. I spent most of that time on my knees on a bean bag on the floor with my head resting on my arms on the end of the bed which had been lowered as much as possible. I had charlotte 40 mins after going to the birthing suite which was only 4.5 hours since the gel had been placed.
I would definately do all you can to stay upright and move around as much as you feel you need to this time and as you say, let nature and gravity do its thing!

Thats so cool you are having a doula in training, i hope i find people to let me attend when i do my training!