I found the techniques great to keep calm and in control of my labour. The MW commented on it. Some of the blurb in the book I found very patronising. I didn't need to feel guilty and responsible because actually I did find my 3 day back to back labour difficult, which is what happened. Some women find that they have no pain at all, which is great for them, but it didn't happen for me, and it makes me sad that the book that helped me stay off the drugs for a very long time ended up making me feel like a failure.
I think it's one of those things that if you can do the classes, then do. But getting as much as you can out of the various books and CDs out there is definitely the next best thing. I would also recommend Katharine Graves of the Hypnobirthing Centre in the UK. She's just produced a book which takes you through everything and has some really good relaxation techniques in there. She also has some CDs too. What I like about her stuff is that she uses a UK perspective and talks about the NHS and what to expect, which I found pretty interesting. But I think what's important is that you find what works for you and what makes you feel comfortable.
I also just read the book - more out of curiosity rather than planning to use it acutally! (And all the way through it I was thinking 'sod this, i'm sooo having an epidural!'). But i ended up practising the breathing loads whilst getting dp to help me with perineal massage from 34 weeks onwards as i found perineal massage really uncomfortable. And then by the day itself i used the breathing techniques quite automatically as I had practised them so much. I had a very quick, calm labour with a little bit of gas and air for an hour but nothing more than that. Midwives and obstetrician were telling me i had hours to go before examining me and finding me fully dilated and everyone assumed i had done a hypnobirthing couse so clearly did something right. i'm pretty neurotic normally and not at all meditation-y so this came as a massive surprise!
So I would recommend finding a breathing technique that you like and practice while doing something uncomfortable like perineal massage (or a hard poo as stowsettler said above). I'm sure some people are naturally blessed with easier labours than others so I'm sure my labour was partly down to luck. But the breathing definitely helped me relax and that only came with practice.
Don't set any hard and fast expectations of yourself in labour though. I don't know a single person whose birth went to plan. That's not to say that they were all bad experiences - just unexpected. For example i was planning to indulge in hardcore amounts of drugs but didn't. On the other hand I have a friend who did loads of hypnobirthing courses but in the end raved for weeks afterwards about how fab her epidural was!
I had a couple of hypnobirthing sessions with my first baby and came across the book when i had my second. Both were drug free births of sizeable babies and think it was the mental attitude behind the hypnobirthing that made it possible. Taking the fear out and trusting in your body helped me a lot.
I've just finished the course (34+4). TBH the main thing is to practice the relaxation techniques and decide which work best for you. Then practice those lots. You only need 1 if 1 is all that works for you. You'll also need to practice the 3 breathing techniques (sleep breathing, slow breathing and birth breathing) - although it's sort of hard to practice birth breathing. My trainer told me to have a go when doing a particularly hard / large poo!! Oddly enough I found it's what I already do. Have a look at the birth affirmations and, if you're anything like me, devise some of your own as the ones in the book / CD are a bit flowery and poncey for my liking. I'm going for basic ones like "My body knows what to do, just follow its lead" and "I'm relaxed, calm and in control". I was amazed to find that just saying this helped me to relax. Obviously I haven't had my baby yet, but I feel very well-equipped having researched and done HB. Most importantly of all it's taken a lot of the apprehension and fear out of me ahead of D-day. Good luck with it - I hope you find it as useful as I do.