Congoo is building audience share in a number of ways. It encourages you to register and create a news circle: a customised list of automated news items about specific topics. This is similar to the automated list of items on the far-right column of this blog. However Congoo focuses on publishers with subscription-based content and its biggest attraction is giving people free access to selected items. Judge for yourself. I have put a link below to a news circle about journalism, online content, and the media in general. Much of it is not applicable to development issues, but you might find something of interest.
Also of interest is the networking element. It is a bit me-too, because it simply adds elements already found in dedicated sites such as Xing or LinkedIn, by encouraging professionals to register their profiles. Such sites have proven to be a useful way to find expertise (or to advertise your CV).
We will have to see if Congoo can find some synergies between the social networking and news items, and any other elements it bolts on.