This has been discussed the past day or two on the blogs hither and yon. Here's one article covering the review of research:
Women 'unprepared for childbirth'
The gist of it is, childbirth educators downplay the pain of labor and women are unprepared for the pain of childbirth.
It's my belief that no matter how well-prepared one is, nothing can prepare you adequately for what labor feels like. I also believe that the typical, default, routine procedures that occur in a hospital birth remove a lot of the natural mechanisms that women laboring may otherwise employ, so that birth is more painful than it may otherwise have been.
In my observations -- the childbirth education I have observed have not de-emphasized pain. The pregnant women I meet realize that there will be pain, and they frequently say in our postpartum meetings that there's nothing that could've prepared them for exactly how it would've been.
What do you think?