According to a recent survey Miami is 29th among the Worlds Richest Cities, by estimated personal net earnings in 2008. And it's fourth among the large US cities on the list.
These calculations are based on wage figures, social security contributions and working hours in 2006 for fourteen widespread professions. Uniform criteria were used with regard to work experience, age, marital status etc. The wage index was weighted by the share of each occupation in overall employment and overall income and also by gender. The figures relate to pay net of taxes and social security contributions. In calculating the 2008 update of the wage index, USB not only took account of exchange rates and inflation, but also factored in that part of the economic growth was due to productivity improvements and was therefore passed on to employees in the form of higher pay.
Of course, Miami is also a leader in poverty. (#1 in a list of poorest American cities with population over 250,000 when ranked by median household income, 2006).
Assuming the validity of the methods — a big assumption — I'm guessing this means we have a low median wage, but a higher average wage due to the presence of a substantial group of some really really rich folks, and of course lots of rich people living off unearned income and/or comfortably retired.
We must have an amazing Gini coefficient.