I don't do rainwater harvesting but am very interested in it. But, most of the systems you buy outright might take decades to pay for themselves and many DIY items are going to be ugly if seen from the street (blue plastic barrels). Add to that, unless you have a way to water using some gravity-feed system, you might be spending more in electricity to operate a pump.
Supposedly 'technically' illegal in Colorado too(due to the way some old laws about interfering with drainage basins or waterways was written?), but, I don't think anyone has been punished that has a rainwater collection system.
interesting thread.