According to IMDB, twenty-one-year-old Sasha Grey, who plays Chelsea, has been in 160 porn films in her three year career! That's not really much indication of her acting talent, of course, but I think she did a pretty good job. It will be interesting to see if she can navigate the waters of more mainstream film, assuming that's what she wants.
The film itself is shot in a lo-fi, almost hidden camera style that makes the audience feel vaguely like voyeurs. But the film isn't about peeping and it isn't really even about the story, which is told out of sequence, intentionally robbing it of much of its drama. No, it's about the characters and about what our desires tell us about who we are.