I definitely agree VT, that it could vary with where you live, but it's an average.
I was just thinking about it from a purely mathematical standpoint...assuming a 28% tax rate that nets about $4500/month, then say you follow the ~30% rule for your rent/mortgage, that's about $1350 to $1500/month rent (that's probably a pretty nice apartment or condo), $700/month for utilities including a cell phone, $300/month for insurance, that leaves you $2000+/month in dispoable income...it's not a glamorous lifestyle, but chances are if you want to go out once in while, or splurge on that nice bottle of scotch, it's not going to hurt very much. Add a spouse and two kids to that income, your definitely on a tighter budget...