Not American, but as I understand it, 401k's are tied to your employers 401k implementation and while you are employed you have little choice in how the funds are managed. If you are contributing to a third party managed fund (employer or otherwise) that is not being matched, then you are ceding control of your retirement funds for no practical benefit. You would be better off putting your savings into another tax shelter appropriate to your needs that you can control.
If you aren't getting a matching benefit or other reward for using an employer managed investment, then you shouldn't. If someone doesn't have the time, inclination, or knowledge to understand the difference then investing in an unmatched 401k is still better than not saving at all :S