I have 4 tanks, 180g, 70g, 65g and 24g. Three were MH and t5 and the 65 was only t5 and the total wattage was in excess of 1800 watts. I had them all of 2011 & 2012. After Christmas in Dec 2012 I switched to all leds. The 180 got 2 IT2080's, the 70 got an IT2040 and the other 3 got Arctic S026's. The total wattage is 960 watts, but they max at about 60% power, so only 500 watts really being used and 3 of the fixtures do long sunrise/sunset so they use even less. They ran all of 2013.
So I saved energy with the lights, my 2 chillers run about 10% as much as they use to run (and they are both outside) and my house A/C runs less. My 2013 total electric bill was over $400 less than 2011 or 2012. I had 6 250w MH bulbs which I replace half every 12 months (3 bulbs x $70 = $210). And I had 10 t5 bulbs which I replace every 12 months (10 bulbs x $20 = $200). So that's $410 in bulb savings and I replace on a conservative schedule. $400+ in electricity savings and $410 in bulb savings = $810 savings in 2013. I got a good deal on my led fixtures in a big group buy and all 6 of them only cost me less than $1400. So I have less than a 2 year payback and I had 5 fixtures I sold after 6 months (just wanted to be sure I liked the leds before I sold them) for $600.
Now I have 4 tanks, 2 chillers and live in SW Florida where we run the A/C 6-8 months (every day), so my savings may be a bit better than most. And I got a deal on fixtures that is still better than most could do today. But a 2 year payback on just savings in electricity and bulbs is incredible. And almost a 1 year if you take the sale of the old fixtures into account (I don't BTW).
There are reasons for running MH or t5 or leds. They all work and they all have advantages and disadvantages. I freely admit my leds have a few issues I'm not thrilled with. But I wouldn't go back to MH if you gave me the fixtures for free! The energy and bulb costs are enough of a reason, but the heat issue was my real driving force. And my 180g DT and 65g frag tank are full of sps and clams that are all just as happy now as they were under MH & t5 combos. Some of you can hate leds all you want, it's your loss IMHO.