Lawsuits based on hiring aren't very common. The main reason is that rejected applicants rarely have access to the information they need to show that the decision was made for illegal reasons -- or even to suspect the employer's decision in the first place.
Everyone has been turned down for a job, and usually it's just because someone better qualified, more experienced, and/or more skilled came along. Sometimes, though, an applicant isn't selected for discriminatory reasons, because of a defamatory negative reference by a former employer, or because the employer considered information it wasn't supposed to have. In these situations, a rejected applicant may have grounds for a lawsuit.