A non-compete is typically for around two years I believe. If they get too broad in length or scope courts tend to limit them or nullify them altogether.
Really, setting any employee in a zero accountability situation and expecting them to act in your interest is irrational... but when the worst an employee can do is hang out on facebook all day rather than working, it's not as big of a deal as the executives who can line their own pockets with much more of your money than most employees take home. Executives can and do take home all kinds of rebates, vacations, and other goodies from vendors.
so yeah, I think the behavior of your typical executive has very little to do with what he or she believes is the best interest of the company.