Bradford Plumer has a post discussing rooftop solar. It mentions Gainseville Florida which has adopted a feed-in tariff which obligates the local utility to buy solar electricity from anyone who produces it. This has produced a flurry of solar power installations which is described as "stunning". However it is considerably less stunning when one learns the tariff has been set (for 20 years for installations through 2010) at the exorbitant rate of .32$/KWh. This means the program is symbolic as it will only be affordable as long as the amount of solar power generated is a small fraction of the power the utility sells.
As I posted earlier I think rooftop solar makes no sense.