Most corporations don't offer enough stock in their employee stock ownership plans for this to really be effective. You have vesting (which means you have to wait before it can be sold) and dilution.

You can also have situations in large corporations where your performance was incredible, and by every measurement you brought millions into the company. However, some guy in division X lost billions and the stock tanked.

There was an AIG employee who wrote to the NYTimes about how his bonus was retroactively taxed 95%, and he claimed it was because of this exact situation. He had nothing to do with AIG's collapse. He was part of a highly profitable division, and was asked to stay on to help turn AIG around faster. That people were upset that he got his contractual 1.2 million bonus was lost on him.