I've been saying this to professionals for years and it is a discussion that keeps coming up.
Larry Bodine posted a summary of a recent Lawmarketing Discussion List thread on whether or not there is value in a Who's Who listing.
Tom Kane, in his May 20 blog post says about adding Who's Who listings to a bio:
From a marketing point, I don’t see it adding very much to your biography. In fact, it may detract from it with those who like Forbes consider it a “vanity publication.”
I think Tom's point is right on and the Forbes article he referenced, entitled "The Hall of Lame" (http://www.forbes.com/fyi/1999/0308/063.html) is pretty good for supporting the argument about why NOT to put Who's Who in ones bio (be patient, though, it will take awhile to download).