Comment The Red Hat Patent Promise and Estoppel (Score 3, Informative) 147
"Red Hat has commited not to sue. So what? Does that mean that they'll remain true to whatever they said?"
Yes, actually, because of the legal principle of estoppel by representation of fact, also known in American law as "equitable estoppel". To wit:
"In general, estoppel protects an aggrieved party, if the counter-party induced an expectation from the aggrieved party, and the aggrieved party reasonably relied on the expectation and would suffer detriment if the expectation is not met."
Red Hat, with its patent promise, induces an expectation: that Red Hat will not sue an open source developer for patent violations. If Red Hat then violates that expectation, a judge would basically throw out any such lawsuit immediately on grounds of estoppel.