I've set most of the lights on timers so they are on until we go to bed (well, midnight) and then on again when we wake up. Not only do they turn off at midnight, but during most of the daylight hours of the weekdays (on all day on the weekends). So far, all of the lights are LEDs, meaning that, including the tree, all of the strands are currently using less energy (and thus also producing less heat) than one strand of conventional Christmas lights.
It certainly makes walking through the house much easier in the "dark," as well as giving it a festive feeling. We still have more that we plan on putting up. My only problem will be that I won't want to take any of it down once the season is over.