The Investment Company Institute has all the data, here.
The old high, before the financial crisis, was reached in 2007 at the level of $17.8 trillion. In 2008 the level of total retirement investments in all categories slipped to a total of $14.1 trillion, a decline of almost 21% as the stock market tanked.
By the end of 2010, however, all the losses were recouped as the level bested 2007 at $17.9 trillion. In 2011 the level climbed again, to $18.0 trillion.
The latest reading in Q3 2012 puts all retirement assets at $19.4 trillion, 9% higher than in 2007, not quite five years on.
The biggest pile of dough, $5.3 trillion, remains in Individual Retirement Accounts, followed by Defined Contribution Plans like 401k accounts, with $5.0 trillion.
Roughly 50% of the American population is not participating in this recovery of retirement accounts because they have nothing in stocks, which under Obama have posted their 4th best performance since World War Two. More precisely, the percentage is probably quite a bit higher than that since just 37% of the stock market is owned by "households", while banks own about 32% of the stock market, the two biggest players if "households" really meant retail investors like mom and pops. It doesn't. But that's another story.
h/t Bloomberg, RushLimbaugh