I guess the problem with demonstrating ability in something is the eventual expectation that you should perform that task again. A few months back, I stepped in and took over the chair duties for a search committee. HR was particularly impressed, at least they said so at the time.
Today I received an email asking if I would chair another search committee, and I accepted the task...here's to a quick and successful search!
Back in 2007, I was part of a very large search committee to find he rector of the church I go to. That was a major undertaking but also a tremendous learning experience. I've used a lot of what I learned during that process in my job and in the searches I have been a part of at work since that time.
I think the only thing I wish I knew in advance before agreeing to chair, or even serve on the committee, is who else was asked to served and more importantly, who else has agreed to serve. Professionally, I know I can handle anyone, but I am at that point in my professional life where if I could choose not to work with some of the more difficult folks, I would.