It would be pretty cool to get a check from the utilities. Also, its nice to have that as a back up power system when you lose power.
The units themselves are not so cheap and I have not heard about lifespan.
I have checked out a few different companies and the pricing is fairly consistant. Just like when you look at buying a new more efficient furnace, you have to figure how many years it will take to pay for it in energy savings. Solar will take many years. I think that there is also a good tax break, state and federal in most states.
I actually worked for a solar company for a couple of years and it can be a good deal, but not always.
First of all, they are the best deal when you're building a new home and you can substitute the cost of shingles, say, for the cost of the panels - solar is still more expensive, but it pays for itself quicker.
Usually, yes, it takes 7-15 years for the cost of the panels to pay for themselves, depending on where you live, how much sun you get, etc...
CA has the most generous subsidies of all the states to defray the initial cost of the system, but most states offer something.
The getting a check from the utilities thing is a bit dicier - each utility has to agree to it, and since it costs them money, a lot are hesitant to do so. Several states (about 30 last time I checked) required the utilities to provide at least some sort of :net metering" provisions so that when you use power from the grid (at night, when the sun isn't shining, or when you have an unusually large power load) your meter works regularly, but when you produce more than you use (during the day when you're at work and your lights are off) you get credit for feeding power back to the grid, which helps with utility stability (remember CA's big blackouts a couple of years ago).
Finally though, I'm glad to see so many Freepers accepting of solar - and not just knee-jerk trashing it as a hippy liberal solution that costs too much money. If you really look into it, it can be a good deal.