California has taken the lead, presumably thanks to the information technology revolution, and continues to hold it despite recent gains of hedge fund money men. Note that counting billionaire fortunes is probably a lagging indicator of wealth (especially in money management -- it takes time to earn your billion there as opposed to a quick tech IPO :-)
We pointed out before that four tech-hotbed counties on the west coast accounted for most of the aggregate increase in national income inequality between 1990-2000.