I have actually changed a great many things in my system due to cost of running the items, but I do the math first. Based on the numbers that are given from LED companies, the cost savings is not that impressive, so I have not changed from MH.
There are a great many things that can be done otherwise to change your bill, well at least for me. For example, I had pumps for everything...i swear every peice of equipment needed a pump. I had 5 tanks lined and there were pumps, pumps and more pumps. I am now running all of the tanks, reactors, etc.. all off of 2 pumps. Reduced average hourly consumption from pumps bu 1/4 (i.e about ...and it cost me all of probably $100 because I wanted to fancy controls. So total cost savings was about $25 a month from $100 spent.
LED Lights wont give you that return. Even with our rediculous electricity rates, it would take me years to recover the cost difference (including bulb replacement). They generally boast about 1/2ish the cost for running, but the up front cost is easily 4x+, and the track record is still waiting to be seen.