I know of several such cases, but it's costly, and usually a good idea to decide whether or not you want to pursue something like this involves the cost (and stress) of a lawsuit over an extended period of time, and to ensure that that is outweighed by the upside of winning the case.

Hard pressed? Ed Saverin is a very well known case. He sued Facebook after his co-founder Zuckerberg diluted him out and settled for multiple billions. But then, it was a unusually straightforward case because Zucks put his malicious intentions in writing.