In Tunney v. Hilliard, 2008 WL 3975620 (Del.Ch., Aug. 20, 2008), the Delaware Chancery Court rejected arguments that a shareholder’s agreement between 50/50 shareholders was orally modified. It also rejected claims of unjust enrichment and promissory estoppel. The factual background involved two men who started a business known as Up the Creek Restaurant and Marina in Wilmington,  with little capital and mostly "sweat equity", but with the understanding that when the business was sold, they would split the proceeds 50/50. The 50/50 split  was memorialized in the governing documents.

The dispute leading to this case arose, however, because during the last few years before the sale, instead of spending about the same amount of time at the enterprise, the plaintiff claimed that he spent more time at the business and alleged, therefore, that he should be paid more for the additional time he spent managing the business–and likewise, he should receive a larger percentage of the proceeds from the sale. In sum, the court found no evidence to support theories of oral modification of the written documents, nor did the court find support for claims of promissory estoppel or quantum meruit.

Moral of the story: If one is expecting to be paid by another, "get it in writing".