I saw an advert from Origin Energy to install solar panels for $4990 (inc. GST and RECs rebate) for a 1.5kw system.
I have no idea if that's good or not, so started thinking about building a solar calculator. Turns out the Solar Shop is way ahead of me there.
Unfortunately their application is a little vague on the details, but suggests around 8-10 years is a typical time period to recoup your losses.
This letter appears to lay out details circa 2001 a bit better.