From the Mouth of Whedon

In an interview with E!’s Watch With Kristin, Joss provides his own description of Dollhouse:

The idea is those with the money or connections can access this secret highly illegal facility where they can basically fulfill their greatest fantasies. Most people assume that means sex - and on an occasion it does, because that is a lot of people’s fantasies - but it’s basically scenarios. They can basically reenact scenarios of romance, adventure or anything perfectly, because they become the person that you want them to be — they become that person. They don’t act like that person, they are not a robot pretending, they become that person, and then they forget all about it. The problem is the character of Echo, Eliza Dushku’s character, stops forgetting. She doesn’t completely remember, but she does realize she is a person, and that she might have been a person before she did this, and she doesn’t know what that is.