It's been a year, and I'm still very happy with the solar water heating system. It's been very dependable, we've never run out of hot water (which is very cool since we have a big family), and overall I think this system offers the best compromise between going tankless vs. using a tank system.
I've come to think of it as a tank system which constantly recharges itself (for free) but doesn't limit the amount of hot water you can use at any given time.
My monthly NG usage went from a monthly average of ~46.5 therms to ~29 therms (about a 17.5 therm savings per month).
Conversely, the KW usage has gone up from a monthly average of 576.5 KW to an average of ~770 KW (~200KW more per month on average).
Depending on the natural gas and electrical rates, one could save money or spend more money with those averages. In the winter, when gas prices tend to be high, we save the most in natural gas usage, but we also used about 500KW more electricity (since the sun wasn't out as much). It works out that if we compare our current PGE bill with our bill from the year before we got the solar water heater, we end up spending less money in the summer on our PGE bill and more in the Winter.
I still feel that the solar water heating system is a good deal for the price you have to pay to have a tankless installed (to code at least), vs. what you pay for the solar setup (minus government tax credits).