Roy Simon calls to my attention a N.J. Supreme Court decision - In re Gormally, N.J. LEXIS 1264 (N.J. Dec. 19, 2012) - sanctioning laweyrs who agreed to a no-sue provision in a settlement agreement. Literally, the agreement violated Rule 5.6(b).
But as Richard Painter and I showed beyond any readonable doubt a few years ago - in FREE THE LAWYERS in the Georgetown Journal of Legal Ethics - Rule 5.6(b) is wrong. From our libertarian perspective, the rule uses state power to prevent the rational economic decisions of those who wish to make an agreement about how they will spend their time. There was a dissent in the N.J.Court but the opinions somehow failed to cite us, perhaps because the lawyers failed to invoke our article. :-)
Some courts have refused categorically to ban agreements limiting practice when a partner withdraws (Rule 5.6(a)) if the agreement is reasonable in light of the economic interests of the firm. So why not permit reasonable restrictions under the circumstances in Rule 5.6(b)?
And oddly enough, as Richard and I show, New York courts, despite the equivalent of Rule 5.6(b) in the state, have disqualified lawyers in order to enfore anti-solicitation and anti-disclsoure provisions in a settlement agreement, which amounts to a no-sue promise in different garb.