We turn off all our desktop computers overnight, two are Windows 7, the other Windows XP. Modem and router are always on, they're on a UPS, since they're serving more than just the desktops.
Can't let my desktop sleep, I'm often on a work VPN and it would disconnect if it slept, and reconnecting is a pain. The other Windows 7 desktop sleeps when it's tired, the Windows XP desktop isn't quite sure how to sleep (or how to wake after sleeping *smile*).