I'm guessing there aren't too many folks familiar with United States employment law among the folks debating and speculating on this list. I submit that this is probably not the sort of thing we want determined by a consensus of amateurs. Lots of people don't like ND agreements, but they don't like binding arbitration, non-compete and non-disclosure agreements either. Even so, they are fairly common and effective. As a matter of fact, I think than an ND for the Board is somewhat less unusual than an ND for employees.
Perhaps the wording of this particular agreement is hasty or inelegant - Board members not at all familiar with American law might reasonably be advised to get independent legal advice before signing binding agreements. (No disparagement [heh] of Mike intended, but he represents WMF and not the Board members individually). Elements of signed agreements like this are somewhat routinely dismissed in court (fairly strict rules on non-compete agreements, limits on the scope of non-disparagement and non-disclosure agreements, etc.), but its still a good idea to know what your rights are and how agreements like this are commonly used in corporations in the US.
Nathan