Do you remember the debate about men saying things like, "but I knew she actually wanted to"? I hear it a lot-- "but I could just tell she wanted it." What happened? Rape. In these very forums I've had arguments with people about how "but I could tell she wanted it" did not translate into consensual sex, and I've had PMs from people sharing their experiences- how they were raped while being told that same line "I know you actually like this."
I do worry that this being super popular, especially among women, may end with some people taking away the notion that "most/many women want to be dominated," which in itself isn't harmful-- until someone doesn't realize that consent, first and before all, is required... since the books make no mention of how consent is the most important thing. & signing that contract wasn't even consent & knowledge, it was some sort of fucked up psychological power play.
edit: Just to be clear, many, if not most, people involved in power exchange (and ESPECIALLY total power exchange), in the BDSM community, are familiar with the burden and responsibilities of a dom. New doms are encouraged to shadow other experienced doms. Being a dom is considered a responsibility and a privilege, and part of that is to be sure that you know what you are getting yourself into, and that your partner is mentally aware of what is going on. I'm not talking about play parties with d/s dynamics, I'm talking about the honestly, somewhat risky business of TPE (which can be awesome). IF the book was a "real" relationship, Christian, being the "experienced" one, is supposed to be partially responsible for educating/discussing with his sub/partner, in a non-power-exchange environment, everything that he and his partner will be doing... to make sure he has her consent when she is not under duress.