How enforceable are non-compete provisions in investment agreements?

finance-maze-2-1211165Private equity and venture capital investment agreements invariably contain provisions imposing non-compete obligations on the promoters of the investee company. These clauses are in the form of elaborate restrictions, prohibiting the promoters from carrying on any similar or identical business to that of the investee company once they cease to be a shareholder or an employee of such company and for a certain duration of time thereafter.