mortgage and health insurance are the usual culprits in the equation
if the 12k/year i spend on health care is out of it (obamacare here i come) i think 40k tax-free would suffice.
the problem is that most people are too busy running in the rat race to think about who designed the race and why they are running in it.
without a mortgage/car loan/student loan you won't be in debt. without debt you probably don't have to work very hard or much.
the guys making $20-30k/year with a family of 4 are just about as well off as the guys making $60k/year when you think about the earned income credits, food stamps, free healthcare for the poor, no real estate taxes for the poor here in wisconsin, free utility assistance, etc etc