A recent Wharton study looked at participants who use Vanguard 401k plans.  It appears the average 401k investor isn't very active with their plan and may not take advantage of all the investment choices.

With $2.5 trillion invested in 401(k) retirement accounts, 60 million Americans control a powerful chunk of cash. So how much attention do investors pay to this vast pool of savings?

Not much.

According to a new Wharton analysis of retirement accounts managed by The Vanguard Group in 2003 and 2004, participants in 401(k) plans made little effort to tend their defined-contribution plans once they were set up: 80% of participants made no trades at all in the time period, while another 10% made only one trade.

The average plan reviewed in the study has 776 active participant accounts with assets of $38.4 million; while it offers over 17 investment choices, plan participants use only 3.5 of the available options. Almost all participants have access to equity index funds (99%) and international funds (98%), but only half of the workers (53%) actually invested in equity funds and only one-fifth (20%) chose international options.