Answering this question I got to thinking, how could we easily identify our areas of core competencies? My initial thought was as part of the blog or wiki, we could identify "regulars" and their areas of competencies/study. That seemed like a high level of effort, so I thought that maybe we could make a recommendation that the "regulars" put a brief blurb about these things in their "about me" on their profile.
Well, you can put anything you like in the "About Me" box. Personally, I don't know what I'd put in there in terms of area of competencies, since I'm an eager amateur and highly unfocused. What I'm studying depends largely on what I'm currently interested in or what books I have at hand.
We don't have a blog (yet?) and I'm not sure which wiki you are talking about. Do you mean the tag wikis? You can get a rough idea of what tags a person has been helpful on in the past by looking a their tag scores. (However it's difficult on this site to separate whether you know something about a particular tag or whether you just happened to answer questions that are tagged a particular way.)
I could see a blog centered around user profiles being interesting. I don't have any other ideas about what we could do with a blog if we chose to create one.