There are many differences of opinion about where the community manager or the community team should fit into the reporting structure of any organization. In general, I think that it depends on the type of community. The community management function should report to the team most closely connected to the audience you are trying to serve.
Too many companies automatically put the community function under marketing, which works well for certain types of communities, but can be disastrous for other types of communities. For example, developer communities or customer support communities should rarely, if ever, report to marketing. However, I do think that marketing should manage the communities for certain types of customer communities or communities that support a specific marketing campaign. Communities focused on a product line could be driven out of a product marketing group.
Developer communities and open source communities should be driven out of a technology or engineering group, since developer and open source communities tend to work best when they are created by developers for developers. Developers in general have very little tolerance for marketing and anyone who lacks technical credibility.
Support communities should be driven as part of the broader support organization to ensure that the customers in the community are getting an appropriate level of support. The support staff deals with support questions all day and are the most appropriate group to be answering the questions in the support forums and making sure that support customers have what they need from the company.
In some cases, the community should report to the senior management of the organization. Some communities cover multiple functions including developers, support, customers, and product information. In those cases, the community team should be placed high enough in the organization to be able to effectively interface with all of the other teams in the organization. If the community is a critical part of the the products or services offered by the company, it might need to be it’s own function within the organization.
It is worth spending some extra time deciding where the community function should be placed within the organization. You need to take a careful look at the audience for your community and place the community in the appropriate organization.