This map was just sent to me and I thought it was worth sharing.  The credit for this image (and lots of other great research and resources) goes to www.dsireusa,org.

Net metering is now policy in nearly 90% of the US.  Net metering refers to the requirement that utilities must compensate you at the same retail price for the electricity you provide them as what they charge you per kwh.  The numbers denote the limits to the size of a net metering system in each state (in kilowatts.)  Here in Washington, our 100 kw limit is preventing the development of many mid-sized or large commercial systems.  The residential and small commercial markets we serve are still relatively immature compared to many other states, but on a healthy growth curve, ie 70% annual growth in number of new systems installed last year, and 50% growth in average system size.