Excerpt: [O]ver the eight-year period from 1999 to 2007: The average 401(k) account balance increased at an annual growth rate of 9.5 percent over the period, to $137,430 at year-end 2007; [and the] median 401(k) account balance (half above, half below) increased at an annual growth rate of 15.2 percent over the period, to $76,946 at year-end 2007. Analysis of a consistent group of 401(k) participants highlights the accumulation potential of 401(k) plans.  MORE >>