My former co-worker, Aaron Newton, is launching this week the product he quit CNET to build: Iminta (as in, "I'm inta," get it?). It's a service that aggregates all your social network feeds into one place, so your buddies can more easily keep track of what you're doing online, and vice versa.
Since Aaron's a buddy, I can't give this product a fair review (see TechCrunch for an opinion on the service itself). However, I did want to point out that Iminta has a cool thing going for it: you can put your followers in groups and specify which group sees what. For example, if you don't want your family to see all your Del.icio.us updates, you can remove that info from your family feed.
When I covered Yahoo's centralized geolocation data service, Fire Eagle, I noted that it had a similar feature: You can let different followers see your data in different resolutions. For example, you could let your family know what town you're in but not precisely where, while making you exact location visible to you co-workers, but only during work hours.
Facebook and other social sites that let you group contacts have crude versions of variable privacy.
I really like the idea of variable resolution for social feeds. Maybe that's because, as an old guy (as opposed to a gen-MySpace guy), I think privacy matters and that it's not an all-or-nothing concept.
I don't think any system has yet made variable privacy manageable. However, it's a new idea, so I wouldn't expect it yet. But if the idea of the implicit social network takes off (see Delver and my take on self-building social sites), we are going to desperately need variable privacy.