It depends upon how the company stock is set up within the 401k, as well as whether you would invest into that company otherwise. Personally, I don't invest hardly anything into the company I work for, due to avoiding the Enron effect. However, there is a possibility that, if your company doesn't provide discounted stock for a 401k, that company dividends are payable as regular income at any age, without the 10% early distribution penalty. This can be a useful tool if retiring before 59.5, and vital if retiring prior to 55.
The key question is, would you invest in your company if you didn't work for them?