Parts of this won't apply to everybody, but we found that insulating our pipes under the crawl space (and setting the timer on our hot water recirculating pump) resulted in savings.
Our house has a system that constantly recirculates hot water so you get practically instant hot water as soon as you turn it on anywhere in the house.
This greatly reduces your water consumption, but it costs energy. In our case, electricity for the circulating pump and natural gas for the hot water heater. The pump has a thermostat so it doesn't run continuously, but it ran a lot. Basically, much of the time it was heating the crawl space where the plumbing is.
We thought about just turning it off. But because of the design of the return pipe system it took a minute or two to get hot water to the shower at the other end of the house, and it wasted a lot of water.
So we did a couple of things. First, we had someone come out and insulate all the pipes. Second, the pump has a timer on it but I had never figured out how to work it. I figured it out and set it to shut off at night. I'm rarely up between 11 PM and 5 AM, so I haven't been inconvenienced by having to wait for hot water that I can recall.
(Most people could probably have it shut off in the daytime when they're not home, too, but we're here most of the time so that doesn't work for us.)
Anyway, we got our first full month bill since doing all that, and it looks like we reduced our natural gas consumption by about 37%. (Except for a gas grill, hot water is the only thing we use natural gas for in the summer. We use it to heat in the winter.)
This works out to about a $14 savings based on a 30 day billing period at the current rates, which by the way have gone up about 6.5% since June of last year. I figure the payback on the insulation will be about 3.5 years, and in the meantime I'm conserving energy. And with the CFL savings, it works out to about $40 per month in savings. We'll see if that holds up over time.
If you have one of these systems, you can save some money by insulating your pipes (the send and the return) and setting the timer to not run the pump when you don't need hot water.
Even if you don't have a recirculating system, insualting your pipes will save energy and money.
The next step is to look into a solar hot water heater...