[Skunkworks] CHANGING JOBS TO JOIN A COMPETITOR

Hi all, I have been wondering if there is a basis in law preventing someone from changing jobs to join a competitor (a similar business). I know most organizations have a clause in their employment contract preventing an employee for working for a similar business for a certain duration of time. But I see it happening in the media industry and Telcos all the time. Also, I remember sometime back a judge throwing out such a case (a media house against some employee) on the basis that the employer could not deny a person the use his skills to earn a living. Any skunks out there who are familiar with the law, please shed some light. Regards, Lenya