There are a lot of good reasons for an employee to be invested in the company they work for and for the company to to want it's employees to own stock.

However, I do think a cap on the percent that can be invested is in order. Something on the order of 20% to 25%. That is a high enough number that it won't get in the way of a sane investor but will keep a person from putting all of their eggs in one basket.

Jay