Most IRA contributions are going into non-deductible Roth accounts, the study reports. "IRAs and defined contribution plans held $7.5 trillion in assets at the end of the year 2006," said Craig Copeland, EBRI senior research associate and author of the May Notes study. "Although Americans have amassed a substantial amount of total wealth in these plans, the data also shows that a majority of Americans still do not have a retirement plan."

In 1985, says EBRI, there were 29,869 401(k)-type plans in the private sector, with 10.3 million active participants with $144 billion in assets. By 2005, the number of plans had reached 436,207. Participants in these private sector 401(k)-type plans had grown to 44.4 million by 2004. Invested assets increased sharply from 1985 ­ 2004, even considering the market volatility of the last part of the 20th century. By 1999, assets held in 401(k)-type plans amounted to $1.79 trillion. With the decline of the stock market, assets dropped to $1.57 trillion by 2002, then increased to $2.4 trillion in 2005.

While the percentage of workers contributing to a 401(k) or similar plan rose in the 21-64 age range, the numbers are not impressive. In 1996, 24.1% of those workers participated in a plan; by 2005, the number was 33.1%. Those contributing the maximum dollar amount allowed by the IRS remains small: 3.2% contributed at the maximum level in 1996, and the figure rose to just 8.9% in 2005.