I recently came across two articles independently that actually come together quite nicely. Leisa Reichelt is credited with establishing the term "ambient intimacy" and has coined a new term she refers to as "ambient exposure" (see the first citation below). Both concepts and the perspective she provides as context came out when I went back and re-read something I had come across earlier (see the second citation below).
The idea of interacting within in a mediated public space (such as Twitter) is clearly an exercise in participatory surveillance. A similar situation arises with services such as Friend Feed. In both cases, I have people "following me" on Twitter or subscribing to my shared activities on Friend Feed, whom I do not know at all. In some cases, this works out well - sometimes the notification that I am being followed causes me in turn, to follow that person if they seem to have some mutuality with my interests. In some ways, these types of mediated public and the ability to establish some level of mutually assured surveillance (reminds one of the cold war term "MAD"), can promote some amount of homophily.
On the other hand, as Leisa rightly points out, it can make one feel uncomfortable as well. Especially when you are followed/subscribed to by someone that you cannot in turn, establish a similar level of surveillance. The sense that there is an unequal power distribution in the relation can lead you to block that person from following you for instance (as I've done at times in Twitter). This situation can lead people to seek certain "walled gardens" (e.g., Facebook) within which they feel more comfortable to share information because such interactions are within a closed circle of trusted relationships whose ties perhaps reflect real-life connections.
Article snippets and citation links below:
It’s been more than a year now since I first wrote about Ambient Intimacy, and in that year it seems a whole lot has gone on.
All of these changes in the past year have gotten me to thinking about something that I’m going to call Ambient Exposure. Exposure in terms of disclosing information of course, but also exposure in the way that a trader might think of it - a vulnerability, a risk associated with taking a position that could, potentially, result in loss or harm.
In the same way that we are not necessarily good at or able to forecast the impact of choosing to add someone to our contact list, we are similarly perhaps not good at anticipating the impact of sharing particular types of information with others.
In the following I suggest using the concept of participatory surveillance  to develop the social and playful aspects surveillance. First, online social networking is related to the traditional hierarchical surveillance concept. Second, the aspect of mutuality will be studied. Third, I will elaborate on the idea of participatory surveillance with regards to user empowerment, subjectivity building and information sharing.
Empowerment, subjectivity building and sharing
In the following, I will call attention to two aspects of surveillance in the context of online social networking which are missing or underdeveloped in the previously discussed concepts. These are the idea of user empowerment and the building of subjectivity, and, second, the understanding of online social networking as a sharing practice instead of an information trade. Together, these two aspects, along with mutuality, makes up what I call participatory surveillance.
As mentioned earlier, a hierarchical conception of surveillance represents a power relation which is in favor of the person doing the surveillance. The person under surveillance is reduced to a powerless, passive subject under the control of the “gaze.” When we look at online social networking and the idea of mutuality, it appears that this practice is not about destructing subjectivity or lifeworld. Rather, this surveillance practice can be part of the building of subjectivity and of making sense in the lifeworld.
Online social networking can also be empowering for the user, as the monitoring and registration facilitates new ways of constructing identity, meeting friends and colleagues as well as socializing with strangers. This changes the role of the user from passive to active, since surveillance in this context offers opportunities to take action, seek information and communicate. Online social networking therefore illustrates that surveillance – as a mutual, empowering and subjectivity building practice – is fundamentally social.
The practice of online social networking can be seen as empowering, as it is a way to voluntarily engage with other people and construct identities, and it can thus be described as participatory. It is important to not automatically assume that the personal information and communication, which online social networking is based on, is only a commodity for trading. Implicit in this interpretation is that to be under surveillance is undesirable. However, to participate in online social networking is also about the act of sharing yourself – or your constructed identity – with others.
Accordingly, the role of sharing should not be underestimated, as the personal information people share – profiles, activities, beliefs, whereabouts, status, preferences, etc. – represent a level of communication that neither has to be told, nor has to be asked for. It is just “out there”, untold and unasked, but something that is part of the socializing in mediated publics.