I sleep nude all year long. It is so much more comfortable not having to wrestling with your clothes under your covers. In the summer time it is cooler and believe it or not you stay warmer in the winter.
Sleeping nude for me is a year round thing. I can't stand fighting clothes when I toss and turn in bed. Being cooler in the summer is definitely a bonus though. As for the winter time I just set the thermostat at 69 F and I'm good.