Adam Douglas Depends. There is a correlation between large-scale, persistently-busy communities and some sort of karma or reputation system. A bone to dangle in front of the dogs, so to speak. On the other hand, such systems elicit some truly crappy behaviour from a community's members. Also, this place takes Twitter, removes the bullshit, improves what's left and returns it as Sublevel. But Twitter does not really have a karma or rep system and I don't think Twitter really suffers for it.

Martijn The problem with having levels is that people might 'gamify' it. Karma brings the inherit concept of bad-karma with it as well, i.e. some actions boost karma and others take it away. I don't think it adds anything to a community. On the other hand if you can indicate real activity that could be cool. These activities are things like 'replying a lot', 'writing a lot', 'always reading' (for people who are logged in a lot but don't post), 'gone for a while' (for people who haven't logged for a while), etc...