I could have written the same post as teaandhobnobs.
I did the 2 day course at 34 weeks, but didnt get to do the second part of the course as baby came to soon.
Got to 9cm dilated within 4 hours, just controlling breathing and using the techniques. Didnt realise!
Needed a bit of gas and air to deliver but i think this was only due to the fact that we hadnt covered the birth breathing in the course (second half) the gas and air did naff all!
Really positive birth experience, felt elated and wanted to do it all again. Second degree tear but was up and about half an hour after we were taken back onto the ward.
Would recommend you doing it for sure but, if you start it at the latter stages of your pregnancy just remember the whole "fear, tension, pain" cycle. That was all that I focussed on throughout the birth and it got me though pretty much pain free.
Looking back I would not say that any part of the labour or birth was painful, just uncontrollable. Id do it again tomorrow!
Good luck x