From lurking to posting - a community participation framework

Are lurkers beneficial or detrimental to a community? Does it make sense to try to convert lurkers into participants or is it just a waste of time and of ressources that would be better allocated e.g. in taking care of new members? Opinions are divided and like in so many cases the answer to both questions is: It depends. Interventions targeted at delurking aren't outright useless. But it seems, that much can already be achieved by setting the right framework for participation.