Feedbuddy is a social network that was bound to happen: one built around RSS feeds. It's actually not a bad idea. As the site says, "subscribing to and reading special RSS-feeds characterizes you and your very special interests." Or in other words, the type of feeds you read has a lot to do with what interests you, so it follows that anyone with a number of feeds in common will likely be someone you share interests with.
In practice, however, Feedbuddy isn't much of a social network. The site is dead simple, and probably shouldn't be categorized as a social network at all. It's more of a rudimentary matchmaking service.
To start at Feedbuddy you simply upload your OPML file or add feeds manually to your "feed profile." You also have to enter a contact method, either your Skype name, Xing profile URL, or web site address. This is important because the site doesn't actually have any interaction features, so if you want to contact any of your matches ("feedbuddies"), you'll need to do so through one of those three methods.
The limited choice of contact methods is a bit odd, however. A true social network needs a way for members to contact each other on site, and the off site methods Feedbuddy supports are not only too few, but strange choices as well. The site is from Germany, which might explain why Xing is supported over LinkedIn, or Skype instead of another instant messenger... but why not both business networks, or more than one messaging application? Adding support for other contact methods -- at least insofar as the site supports the current lineup -- would only be a couple of lines of code.
Feedbuddy has a good idea; matching people's interests based on the feeds they read makes a lot of sense. But as a social networking site it seems rather half baked right now, and it feels a lot more like a feature than a full on web site. I would suggest the Feedbuddy crew consider creating a Facebook application. That would not only solve the problem of being able to contact members through the site (users would just utilize Facebook's system), but also might expand the userbase, which seems a bit tech-centric at the moment, more rapidly and allow for more meaningful matches.