I bought a 5 kw system in houston for $2.75/watt. The ROI depends on what kind of credit you can get from your local retail electricity provider. With standard net metering, solar panels are probably a good deal (pay for themselves in <10 years, and then you get 20+ years of production from them).
But, in some areas of the country, utilities are pushing back against net metering, as it is unfair to them. Roughly 1/3 of the price you pay for electricity is electrical generation, 1/3 is grid maintenance, and 1/3 is billing/customer support. Net metering doesn't compensate the utility for the latter two things. That is why utilites have succeeded in adding a fixed monthly charge to some solar customers in some states (AZ). I see this spreading to other states as solar becomes more popular.
In Houston, Reliant used to have a plan that compensated me $0.17/kwhr for production, and only charged me $0.10/kwhr for consumption. Obviously, I took this plan straight to the bank and have ended the year with a $300 credit that I will get in cash back. Now, however, they have adjusted the plan to pay only $0.07/kwhr for production, and charge $0.14/kwhr for consumption. Not nearly as good! I am switching to Green Mountain Energy that offers a more standard net metering plan of $0.12/kwhr for both production and consumption.
I like my system so far, but potential problems I can see in the future are:
1. Further changes in net metering plans to become less generous
2. Additional costs to uninstall and reinstall panels when it is time to get a new roof
3. Microinverter failure and replacement
4. Will it scare people from buying my house when it comes time to sell? (or conversely, it could make it more attractive to some buyers...we'll see!)