social media and online engagement

We are looking at venturing into some new areas (and maybe new technologies) that enable deeper engagement and more interaction online with our patrons, members, sponsors, and the community at large. Some specific questions I have are:

Do you have online spaces for dialogue with members and/or patrons? Many organizations have blogs where people can comment. But in general blogs are more about one-way broadcasting. What about forums where there is greater exchange between people online?

Do you have members-only web content, and if so, what is it?

Do you use social media for fundraising - using social networks to get people involved in an event or do some of the actual fundraising through their networks?

Do you use LinkedIn? As a professional networking site, it seems like it might be ideal to deepen relationships with sponsors and their employees, for example.

Any thoughts/ideas/opinions are much appreciated. Thanks!