A lot. My expenses (having moved from NZ) are probably 2-2.5x of what my friends back home pay - and I don't live a particularly frugal life. My income is 4-5x (probably even higher) what they make. Tech people on HN in the Bay Area talk about saving $25-50k / yr. The average household income in America is roughly $50k.

*Caveat: I'm unmarried and don't have kids. I don't own a house yet. I think that might change the equation a bit.