1. What are the benefits and costs of lurking?
Lurkers are users on the fringe of a community, who observe but don't interact. Here, the word 'community' is used in a wider sense and designates any virtual meeting place where people with common interests communicate. A sense of virtual community is not required.
Some research points to the existence of potential benefits to the community:
- Lurkers may be silent individuals but nevertheless they are an audience for the community's concerns. 
- 'Active' lurkers on the fringe of one community may spread information as contributors to another. 
- Lurkers use the available information and by doing so relieve the community from answering the same questions over and over again. 
- On the other hand, lurkers are viewed as free-riders or social loafers who let others do the job and - worst case - who keep the community from reaching a self-sustaining level. 
But all things considered, a healthy community should not fear lurkers and profit from the beneficial effects.
2. Why do people lurk online?
In several studies [5, 6, 7], lurkers, their reasons for lurking and their relationship with the community have been examined. Here are some of the results:
- Whether a person joins a public (special interest) community depends mainly on his/her personal reasons (other reasons may be work- or school- related.)
- There are some reasons for joining an online community that lurkers and participants have in common (e.g. getting a general understanding of the community, reading conversations/stories). But participants seem to be much more attracted by the prospect of engagement in the community (be a member, make friends, offer one's expertise, get empathetic support).
- A person may contribute to one community and be a lurker in another. The behavioural outcome is dependent on the person's overall engagement (a trait!) and strongly modified by the person’s attitude toward the topic, the community or the task. 
- Futhermore, lurkeers seem to have much less satisfying experiences with the community and report that they get less than the expected benefit. This of course results in a lesser sense of community and lurkers are less likely to consider themselves as community members.
One study  from 2006 offers interesting details. In checkbox questions and open-ended questions lurkers were asked to tell more about their reasons.
Reasons why lurkers don't post (Checkbox Questionnaire; % of respondents [N = 219])
- Didn’t need to post
- Just reading/browsing is enough (53.9)
- No requirement to post (21.5)
- Had no intention of posting (13.2)
- Needed to find out about the group
- Still learning about the group (29.7)
- Thought I was being helpful
- Nothing to offer (22.8)
- Others have said it (18.7) Others respond the way I would
- Couldn’t make the software work
- Not enough time to post (9.1)
- Do not know how to post to this group (7.8)
- There are too many messages already (4.6)
- Didn’t like the group (poor dynamics/fit)
- Shy about posting (28.3)
- Want to remain anonymous (15.1)
- Of no value to me (11.0)
- Poor quality of messages or group/community (7.8)
- Wrong group (7.3)
- [observed] Long delay in response to postings (6.8)
- Concern about aggressive responses (5.9)
- Fear of commitment/If I post, I am making a commitment(4.1)
- Group treats new members badly (1.4)
Two aspects should be highlighted:
- Only 13.2 % of those questioned had no intention to post from the outset. From this, one can infer that there is a considerable number of users who loose interest in contributing while lurking although they even might have had the initial intention to participate.
- Not every reason for lurking can be targeted by community management (e.g. not enough time to post). And many reasons that can be influenced (e.g. long delay in response to postings) are certainly already on the agenda of every committed community manager.
3. A community participation framework
The framework  has four different levels. It starts with the lurker's motivation which influences the goalsetting and the expectations. The perception of the community has the final say whether the lurker thinks that his/her expectations will be met and his or her goals will be reached. It is important to keep in mind that this is not a statistically tested and proven model. It rather aims at showing potential intervention points for community managment. It hopefully helps design, structure and prioritize programs and policies for guiding a silent user towards participation.
- Top-down: A specific user motivated by a special interest (e.g. a health care issue) looks for an appropriate community. The intention is to find out more about a special treatment and to ask questions about it. Browsing the community he/she matches his/her expectations with what the community has to offer. If there is a match the user will stay and further investigate the community and eventually become an active participant.
- Bottom-up: The reaction of the community to the newbie's participation, in turn, confirms or modifies the perception of the community and the user's expectations. This might lead to a change in the user's goals and ultimately in his/her motivation.
Although, theoretically, community management could try to adopt measures to intervene on each level (e.g costly sweepstakes to foster extrinsic motivation), its main approach should be well-designed contact points where the users and the community meet (e.g. an easy-to-use technology, intuitively structured community sites, a open-minded ambiance, motivating posts for newbies, community members who are tolerant in their dealings with one another etc.).
4. Can community management convert lurkers to posters?
According to social learning theory (=people learn from one another, via observation, imitation, and modeling) a new community member will start as a lurker or with relatively few contributions. Over time, the new member gains knowledge and confidence, and begins to contribute. The contributions increase as the member develops competence and confidence.
One such 'evolutionary path' could be described in this way: A new member would start as a visitor (lurker). Becoming a novice he/she learns the norms of the community, builds an identity and, later on, becomes a regular, who participates reliably in community life or even a leader who keeps the community running. The highest achievable position would be an elder, a long-time regular and/or leader who is estimated for sharing his/her knowledge. 
This sounds very promising because it seems to offer an opportunity to develop one's community in some kind of life cycle model. To my knowledge - and unfortunately - the prerequisites for a successful conversion of lurkers to contributors have not yet been examined. In my opinion once again the person's overall engagement and attitude toward topic/community/task are the decisive factors.
Suggestion for further reading
- For a concise version, see the post "Can community managment influence lurking behaviour?" on The Community Manager
 Rafaeli S., Ravid G., Soroka, V. (2004). "De-lurking in virtual communities: a social communication network approach to measuring the effects of social and cultural capital". Proceedings of the 37th Hawaii International Conference on System Sciences. Google Scholar
 Takahashi, M., Fujimoto, M., & Yamasaki, N. (November 2003). "The active lurker: influence of an in-house online community on its outside environment". international ACM SIGGROUP conference on Supporting group work. pp. 1–10. Google Scholar
 Lakhani, K., von Hippel, E. (2003). "How open source software works: Free user to user assistance". Research Policy 32. Google Scholar
 Kollock, P., Smith, M. (1996). "Managing the virtual commons". Computer-mediated communication: Linguistic, social, and cross-cultural perspectives: 109–128. Google Scholar
 Nonnecke, B., Andrews, D., Preece, J. (2006). "Non-public and public online community participation: Needs, attitudes and behaviour." Electron Commerce Res 6, p. 7-20. Google Scholar
 Nonnecke, B., Andrews, D., Preece, J., Voutour, R. (2004). "Online Lurkers tell why." Proceedings of the Tenth Americas Conference on Information Systems, New York, New York, August 2004. Google Scholar
 Nonnecke, B. & Preece, J.. (2001). "Lurker demographics: Counting the silent." Proceedings of CHI 2000. The Hague: ACM. Google Scholar
 Muller, M. (2012). “Lurking as Personal Trait or Situational Disposition? Lurking and Contributing in Enterprise Social Media.” CSCW 2012, February 11–15, 2012. Google Scholar
 I adapted this framework from Bishop, J. (2007) ["Increasing participation in online communities: A framework for human–computer interaction". Computers in Human Behavior 23 (4), p. 1881–1893. Google Scholar] and Preece, Nonnecke, Andrews, Voutour (2004).
 Kim, Amy Jo (2000). “Community building on the web.” Berkely; Peachpit Press. Google Books