Central reference for numbers here, the source is tweeted by ~5k and Facebooked by 36k so I have some confidence in the numbers.
http://www.politifact.com/wisconsin/statements/2011/mar/10/michael-moore/michael-moore-says-400-americans-have-more-wealth-
First some prelim calcs for the bottom categories for population size:
400 billionaires / 308,745,538 (census 2010) = 0.000129%
9,800,000 millionaires / 308,745,538 = 3.17%
185,247,323 poorest 60% / 308,745,538 = 60%
America's total net worth:
$56.8 trillion (federal reserve)
Forbes top 400 (% population: 0.000129%):
$1.37 trillion
9.8 Millionaires (% population: 3.17%):
$31.80 trillion
Poorest 60% of USA (% population: 60%)
$1.26 trillion
Remainder missing:
100% pop - 0.000129 - 3.17 - 60 = 36.82%
36.82% of 308,745,538 = 113,668,693
$56.8 trillion - $1.37 - $31.80 - $1.26 = $22.37 trillion
Remainder's net share: 22.37 / 56.8 = 39.16%
So, in a nutshell:
Forbes top 400: 0.000129% pop
... Controls 2.41% of total net worth
9.8 millionaires: 3.17% pop
... Controls 55.98% of total net worth
Poorest 60% of USA: 60% pop
... Controls 2.21% of total net worth
Middle class, upper class: 36.82% pop
... Controls 39.16% of total net worth