Zappos.com, the online seller of shoes and clothing, saw participation in its 401(k) plan jump from 19% to 39% after it revamped the plan's governance and investment lineup and instituted automatic enrollment.

Few changes had been made to the 401(k) plan since it was started in 2003, and in 2008, Zappos decided it was time to clear away the cobwebs. At Zappos, "our first core value is to deliver wow through service," says treasury analyst Scott Schaefer. "We wanted to do that internally, we wanted to deliver the wow to our employees."

The human resources department decided to start automatically enrolling new employees at a 1% deferral rate, using Fidelity's target-date funds as the default investment. (The company has not offered a match because it said it would rather use that money to fund other employee benefits.) Zappos also created an Investment Policy Statement, which put in place a plan advisory committee.