I admit that I was initially disappointed when I realized that the flashbacks in this episode were from Juliet's past. "Let's get back to the main characters," I thought. But this turned out to be an outstanding episode.
A good amount of information about the Others was revealed during Juliet's flashbacks. We see how she was brought to the island, a bit of the leadership structure of the Others, and the research she does there (which in turn reveals that the Others don't get cancer but that women who are pregnant on the island do not survive). We also see that the Others are able to closely monitor outside civilization.
In the present time Jack, Sayid, and Kate return to camp with Juliet. Most of the survivors don't trust Juliet (especially Sawyer and Sayid) but Jack vouches for her. She attempts to earn their trust by saving Claire's life. The last flashback (which occurs right before the time of the previous episode) reveals another plot twist.