I swithched from a grundfos pump on demand to a jet pump / pressure tank system thinking I would save electricity since the grundfos starts up every time water is called for. Does anyone know if I did the right thing or if I wasted my time and money?

Its hard to say. Really depends on your system. How much water you use so on so forth. I really don't think that you will see much(if any) savings on your electrical bill. The on demand grundfos pumps are a good pump(if you are talking about an mq3) It really comes down to space saving(as the grundfos takes up very little space, as it doesn't require an additional pressure tank). And it maintains a more constant pressure(because it is operated off a flow switch rather than a pressure switch) And noise, because the grundfos is much qieter than a standard jet pump. But don't get me wrong. If you don't mind the noise, pressure fluctuation, and space issue, jet pumps with pressure tanks can be just as good(if not better in certain applications) than the on demand pump. Overall, if you are happy with the change, just don't lose any sleep over it. Its all good.