If we examine sex as a political act, something that flies in the face of cultural or political expectations, it is from this point where much of the discussion can develop. In social or political orders where sex is seen as something forbidden, something taboo, or something that is frowned upon, one can see parallels between these settings and Winston's contention that Julia was a rebel "from the waist down." Sex is an act of rebellion in Orwell's work because it is something that is forbidden, a private act that has been appropriated by the public. It is in this light where it is seen as an act of subversion. Hence, in different settings that are inward in their socially gravitational pull, there can be much in way of similarity between how sex is viewed in Orwell's novel and in these realms. When examining the cosmopolitan and widely accepted belief that sex is a private act, the similarities become a bit more murky. On one hand, when sex is relegated to the realm of the private, there is little ground for rebellion. When the public realm disavows the desire or need to control this realm, the activist theme disappears. There can be an argument made that sex has become so publicized that there is a desensitivity to it. In this light, perhaps the notion of viewing sex and something other than what it actually is might be another similarity between Winston's perception and the modern setting.
I would say that the more interesting element here might not be the sexual activity and paralelling it to the modern predicament, but actually examining the theme of renunciation. Winston and Julian both renounce one another when confronted by the interrogation room. Two people who shared the most intimate of moments, the most tender of instants, end up renouncing the other and betraying one another. While we are repulsed by it, we understand it, to a certain extent, because the use of terror was quite precise. Yet, when we see the same behavior in the modern setting, where the external use of terror is absent, I think that it becomes quite scary because we, in a way, have become our own Big Brothers, our own tormentors. Perhaps, this was another one of Orwell's points being made. In our own behavior towards one another, Big Brother is not something separate from us, but rather walks amongst and within us.