dexprs, when thinking about the proportion of one's investment in company stock, just think "Enron". I'm retired from another Big Energy company where Ken Lay was our No. 2 man before he moved along to become the chief at the newly formed Enron. Lay was a likeable and admired man, and it would've been unimaginable for any of us to think of the financial devastation that would eventually happen to Enron's employees and retirees under his leadership.
Diversify, diversify, diversify. It can't be said enough, IMO.