Don't hot water recirculating systems waste water?
Even though you may get faster hot water to the faucet, doesn't the cold water line now have hot/warm water in it? Won't you waste as much water waiting for it to get cold?
It really depends on the type of hot water recirculation system you have.
The better systems have a closed loop on the hot water side so the hot and cold water do not mix. This definetely saves water -- without a recirculating system you have to "flush out" the cold water while waiting for the hot water to come to the faucet/showerhead, etc.
Some retrofit recirculating systems do use the cold water line as the return line to the water heater. I believe the theory is you save water when you need to use hot water. When using the cold water, often having warm water come to the faucet will not be a problem -- washing hands, washing dishes, etc.
Rarely would you need truly cold water so only on rare occurrences will you need to flush out the hot/warm water -- but the savings from not having to flush out the cold when using hot water will by far outweigh the few times you flush out the hot.