Enthusiast communities are, for the most part, driven largely by ego. PR experts post in PR forums or blogs because they like to share what they know. It feeds their ego to show off a bit, or perhaps to help other people and get that kind pat on the back from someone they’ve helped.
Enthusiasts communities are based on emotion. Nearly everyone online isn’t required (by law, job description, or anything else) to be online reading and writing blogs, or posting comments on blogs, forums, wikis, etc. They’re doing it because they get a kick out of it. It’s either a dedicated hobby, or a hobby-like interest.
When you interact with an enthusiast community, it’s often hard not to slid into "professional mode". We’re not used to having to cater to other people’s ego on the scale we have to with online community in the rest of our work day. One of the reasons that I think old school marketing and PR people find it so hard to get this interaction right is because they’re not use to having a more personal relationship with those people associated with "work". There’s an expectation that since the business person is at work, the community member(s) should be too.
Look at PR people, for instance. Until lately, the only people they’ve had to work with are colleagues (internal professionals) and journalists and other media contacts (external professionals). Now along comes a community member who’s never worked with a PR group or as a journalist, and before you know it, both parties are missing each other’s desires and mindset entirely.
Of course, entering into a community and expecting that they’ll act like contractors or clients is a recipe for disaster.
Treat community members like friends, not co-workers. Stroke their egos, show them your own human side, tell them their projects are great (because most likely they are anyway). A pat on the back "buys" you more in the online community than $100,000 worth of merchandise ever will. Remembering their names every time you meet them will get you further than anything else.