Some data to consider:
Advantages: Use for projects of associations, organizations and projects without profit spirit.
Disadvantages: Less coherent for use of personal sites or businesses.
Something of history:
The .org domain was created in January of 1985. Originally it was created for the organizations who are not classified suitably in the other domains. At present they do not exist requisite specific to register it. Usually they are used for associations without spirit of profit, NGOs and projects of free software, as opposition to .com that use the companies habitually.