In 2003 Norway introduced a law mandating that at least 40% of a company board be composed of women (at a time when the average was 9%). Before you ask no, there was no provision regarding "under-representation" of men, so you're free to open a gurrrl power company if you wish.

One might wonder what the effect could be of imposing hiring not on the basis of merit but on the basis of genital configuration:

http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1364470

tl;dr: stock price dropped, Tobin's q (a measurement of how much the market values a company besides its assets, i.e. the company as an organization rather than the company as what it owns) dropped, companies increased in size and started more acquisitions (especially in the latter years to try to combat drops in valuation), increased leverage (the liabilities/assetts ratio), reduced cash holdings, overall worse performance.

A literal across-the-board disaster. Unfortunately the paper doesn't delve into the mechanics of how these new "gender-balanced" boards operated and what caused the drop in performance, although it's hard to imagine that it had nothing to do with the new average 31% of female board members given how vast and pervasive the problems are.