I met with Mario Sundar, a great guy and currently the Community Evangelist at LinkedIn yesterday. According to him there are 3 aspects to getting compelete feedback from his community:
1. The online community and his forums area
2. Blogs
3. Offline events

Triage on these three he says and you will get comprehensive information about what the community of customers and influencers need.

His role according to him is primarily involves interfacing with customers and users of LinkedIn and ensuring their voice is heard by the Product Team, Executives and Marketing.

Here is another link to Amazon’s web services (from Jeff) evangelist that you might find interesting. It details what’ expected from that role. Highlights:
1. Speaking Engagements
2. Blogging
3. Writing White Papers
4. Attending and managing Developer Meetings
5. Press Interviews
6. Building Sample Applications
7. Hosting Screen Casts