So much for Silicon Valley's latest get-rich-quick scheme. Facebook CEO Mark Zuckerberg has cancelled a plan to let employees cash out their shares early. In August, before the markets started to melt down and with Facebook worth $15 billion on paper, Zuckerberg unveiled a plan to let employees sell a small amount of their shares — no more than $900,000 or 10 percent of their stock holdings, whichever was less. The program, all but unheard of among Valley startups, was meant to appease employees who were agitating for some chance to make money from their shares. It was a revolutionary new way to reward employees, without having to go through an IPO or a sale.