The cost of solar electric installations has dropped in the last year but so have the rebates.  The following article gives an example of the costs and benefits -

12-12-09 - Is Solar Power a Good Investment?

NOTES:

Solar System: Modules assumed are Evergreen 205 watt (DC); SMA-America inverter (no battery backup); aluminum racking system mounted on 4/12 composition shingle roof; modules located in area free of shading; dirt on modules was assumed to reduce solar gain an average of 5%.
Incentives: Current rebate is $1.10/watt (AC) and the Federal Tax Credit is 30% of the system cost (after rebate).
Financial assumptions: Home Equity Line of Credit (HELO), 7% fixed for 15 years with no points; Married couple filing jointly with $100k/yr annual income; 30 year investment period; electricity cost escalation rate 6%.
Rate Schedule: E1 (original) to E6 Net Energy Metering (NEM) available for customers of PG&E.
Analysis Tool: We used Quick Quotes from Clean Power Research, the best tool we know of for energy and economic analysis of photovoltaic systems.

Factors that will increase economic benefits: Longer loan period, low fixed rate on loan, and/or an electricity escalation rate above 5%. While the historical escalation rate (last 30 yrs) was 5% we strongly believe it will be much higher over the next 30 years; therefore, to be conservative, we've used 5% for the above analysis.

Factors that will decrease economic benefits: Paying cash instead of financing at a low fixed rate (due to mortgage interest deduction benefits). A variable rate loan (if interest rates rise over the loan period). Shading from trees and/or a lower rate of electricity cost escalation. Systems mounted on pole tops or ground-mounted arrays, which cost more than the assumed roof-mounted system, will be more costly initially; the added cost is generally returned when the cost of removing (and reinstalling) a roof-mounted array (during a re-roof) is considered. Standing seam metal roofs cost the same as a composition shingle roof while tile roofs are slightly more expensive (new construction) to considerably more expensive (existing construction).