According to Apple's market and the general PC market in fact, most people are buying laptops rather than desktops these days. Laptops by their very physical nature are put to sleep when a user is away from them.
I think more people are running home servers than ever before though. I personally a computer sitting in the basement running 24/7 as a media centre.
I like the combination of the two. So have the basement server machine as an always on device (can do screen sharing to it etc), with the laptop as the take-away device when you need it.