PensionReforms' summary and comments
The EBRI produces a regular summary of statistics on Tier 3 schemes in the US.  PensionReforms looked at the 2006 401(k) survey here.  This latest report looks at the 2008 data.  The survey covers 24 million members employed by 55,000 employers and covering $US1.1 trillion.  It apparently "covered 48 percent of the universe of active 401(k) plan participants, 12 percent of plans, and 47 percent of 401(k) plan assets."

It does not include "Individual Retirement Account" data (IRAs). 

The report looks at 401(k) balances, allowing for contributions so we cannot see the direct impact of investment returns and perhaps that's not particularly useful given that participants can usually choose their investment strategy.

Across all participants at the end of 2008, the average account balance was $US45,519 (up from $US37,323 in 1996) but the median balance was only $US12,655 (up from $US11,600 in 1996), indicating a considerable skew in balances.  In fact, about three quarters of all participants had a balance in 2008 of less than the average amount of all participants.  PensionReforms thinks that both the small median balance and the very small difference in nominal values over the 12 years to 2008 (+22% for the average and +9.1% for the median) seem quite remarkable.

However, as the report notes, members with at least five years' membership are probably more interesting:
"Because 401(k) balances can fluctuate with market returns from year to year, meaningful analysis of 401(k) plans must examine how participants' accounts have performed over the long term.  Looking at consistent participants in the EBRI/ICI 401(k) database over the five-year period from 2003 to 2008 (which included one of the worst bear markets for stocks since the Great Depression), the study found:
.  After rising in 2003 and for the next four consecutive years, the average 401(k) retirement account fell 24.3 percent in 2008.

.  The average 401(k) account balance moved up and down with stock market performance, but over the entire five-year time period increased at an average annual growth rate of 7.2 percent, attaining $86,513 at year-end 2008.

.  The median (mid-point) 401(k) account balance increased at an average annual growth rate of 11.4 percent over the 2003-2008 period to $43,700 at year-end 2008."

Despite the terrible returns from shares in 2008 (the S&P total return index, for example, fell 37% in the year), by the year-end, 56% on average of 401(k) participants' assets were invested in shares and 41% in fixed interest style investments.

"Across all age groups, more new or recent hires invested their 401(k) assets in balanced funds, including lifecycle funds.  At year-end 2008, 36 percent of the account balances of recently hired participants in their 20s were invested in balanced funds, compared with 28 percent in 2007, and about 7 percent in 1998.  At year-end 2008, almost 23 percent of the account balances of recently hired participants in their 20s were invested in lifecycle funds, compared with almost 19 percent at year-end 2007."

On average, only 9.7% of balances were in employer stock, down 1percentage point in the 12 months.

Members of 401(k) schemes can borrow money from the scheme:
"In 2008, 18 percent of all 401(k) participants eligible for loans had a loan outstanding against their 401(k) account, the same percentage as at year-end 2007 and year-end 2006.  Loans outstanding amounted to 16 percent of the remaining account balance, on average, at year-end 2008; this is similar to the year-end 2002 level."   (File size 822 KB;  68 pp)  349