When I go to the listing for Debevoise & Plimpton LLP in Martindale-Hubbell, I see the blue LinkedIn icon next to the name of the firm. If you click on the icon, it asks you to logon to LinkedIn to see who you know at the firm. After logging on I get a pop up that shows my two first level LinkedIn connections (Mary Abraham and Patrick DiDomenico) and a total of 131 connections through the second and third level.
Assuming clients are still using Martindale-Hubbell to find law firms and lawyers, this make the directory much more powerful. (Of course that is assuming that clients still use Martindale-Hubbell.) The interface is a bit kludgy, but the information is great. The LinkedIn connection also appears when you look at the listing for some individual lawyers.