This paper reports the results of a study into a public space Internet portal which publishes guitar tabs (tablature) online, to examine what motivates people to participate in this activity and what benefits they get from doing so. A guitar tab is essentially sheet music for guitarists. The study examines why people contribute when it is easier for them not to publish their tabs and simply use the tabs that other people have posted. Answers to this will have implications for businesses wanting to encourage their employees to share their knowledge. An open ended questionnaire was sent to 183 tab publishers with a usable response rate of 39%, which is considered high for surveys. The questionnaire sought to gather data on motivations, benefits and community interaction. The paper begins with a review of relevant theories of knowledge sharing and publishing, in particular the private-collective model of innovation (von Hippel & von Krogh, 2003) which is used to analyze the results. Motivations are listed as under two categories, self and altruistic, with the most popular motivation being to share the songs with others, which is from the altruistic category. The most common benefit is personal satisfaction. The results show tab publishing fits with the private-collective model of innovation which means that a tab published online can be seen as a public good, as it is available to all, that has significant private elements. These private elements are the benefits that tab publishers get which the people who only use tabs without contributing their own, do not. The implications of the work are as follows. Enjoyment of the domain seems to be an important factor in motivating knowledge sharing. People who feel like they are part of a community and get satisfaction from being part of a community, will be more likely to contribute. The act of sharing knowledge should be as close to effortless as possible to encourage contributions. The act of preparing (collecting, collating etc.) the material to be shared should have meaning in itself for the person who is preparing it. If the act of sharing leads to increased status in the community people will be more likely to contribute. To encourage knowledge sharing, those who make use of the shared knowledge should be encouraged to give positive feedback to the person who shared it. To date, there has been little empirical work examining online posting forums.