Do not not not forget to diversify, hello Enron. You might give up some gain, but you will also be mitigating risk.
There is one large employee-owned I know of that I wish would go public because I would love to have a piece of it. Awesome company, very successful, very innovative - there is no way this company can fail. There's also no way I would put more than 10-20% of my life savings into them no matter how awesome they are. Things happen.
EDIT: one more thing for anyone under the age of 30 - max out your 401K contributions now. Just do it. Trust me. It'll only hurt a little in the beginning, and then you can scale it back in 10 years if you want.