I researched this a few months ago for the same reasons you are. The ROI is very long usually. A good size setup supposedly costs like $30,000-$60,000, and only generates about $0.20/hour worth of electricity (2KW at approx $0.10/KWh), so even if you figure the cheap end at $30K, and assuming 12 hours per daylight per day, and double the output at $.40/hr, that's still a 17 year break-even.
Maybe Jersey has more tax breaks than here in GA though. Those estimates aren't even factoring it in.
My problem is that I have no idea if I'll even be in the house for 17 years, plus I have no idea if the panels even last that long... I'd be pissed if they broke after like 8 years... or 10/... or 16.9 years...