For Christina Kerley (CK) it's Paul Newman's pasta sauce. For me it's things like Listerine toothpaste, Thorlo socks and a host of other tics that I won't bore you with. And tics is an apt descriptor, since for many of us, our devotion can best be described as a Larry David-esque tic, an irrational devotion to a certain brand that transcends logic and rational thought.
Now for marketers, the fact that even Thorlo socks can have a brand evangelist (and I have been known to preach to people, especially people who engage in strenuous athletic activity, on the benefits of Thorlo socks) is significant in that we need to figure out how to reach these people.
Advertising isn't worth it for them-- they know, far more than you do, why your product is so great. They don't need reminding. (Unless, of course, you've got some news for them about a new product line or innovation.)
But they're also not going to go on a brand-specific social media site and start participating. Your brand is not one they see as an intrinsic part of who they are (which is the way they view true Prom King Brands like Nike, Apple and Starbucks) but rather as a relevant piece of knowledge they have (e.g. "Paul Newman sauce is better than any other sauce.")
That's why you've got to engage them elsewhere.
Using my Thorlo socks example, I'm not going to start participating on SockBlog. But I may write something positive about Thorlo on a running blog like Internal Pigdog. And I'm guessing I'm not the only one. So maybe you take us and put us on a consumer advisory board. Give us a bunch of free socks for taking an hour to talk to your research or product development people. Something that acknowledges our devotion to your brand without forcing us to make you a part of our identity.
I suspect it would be well worth the effort.