I've seen this news story mentioned several times this week, about a lawsuit settlement agreement that fell apart after a court held that the plaintiff violated the confidentiality clause in a settlement agreement. More specifically, it was the plaintiff's daughter who shared information about the settlement via facebook. The result, according to this news report from the Miami Herald, is that funds totaling $150,000 ($10,000 for back wages, $80,000 as settlement of other claims to the plaintiff and $60,000 to the plaintiff's lawyers) will not be paid by the defendant. Other news reports are here and here.
Most settlement agreements contain confidentiality clauses that prohibit the parties (both sides) from discussing the specifics of the settlement. Some specifically limit disclosure of the settlement to a standard, non-descript phrase such as, "We have settled the matter on a confidential basis." Usually, there are carve-outs so that the parties can share vital information with their accountants, tax advisors, and lawyers, but the agreements otherwise restrict communicating the details of the resolution beyond that. Simply put, the parties agree that other folks don't need to know the details and agree to keep the terms of the resolution confidential. And that can benefit both sides.
Yes, confidentiality clauses in contracts can be enforced (and a settlement agreement is a contract). It has some teeth, and can bite you if it is violated. That can be a very costly lesson for some.
The take-away lesson here is this: be sure you understand what you have agreed to do, or not do, when you've entered into a contract with others. And understand that violating those provisions can have some serious consequences.