I urge members of LinkedIn to join my group, Law Department Management. We have more than 250 members and welcome everyone.
Foraging more widely on LinkedIn, I have found at least 35 groups for lawyers. Not in-house counsel exclusively, but lawyers or support functions for lawyers. In the aggregate, tens of thousands of LinkedIn people are members of those law-related groups (See my post of Sept. 22, 2008: social networks such as LinkedIn, with 7 references.). Others certainly exist, unknown to me