With the exception of the cable modem, I am a "switch off" man. Overnight, everything is switched off (occasional AV scans excepted) but not unplugged.
Away on holidays, almost everything is switched off at the mains and unplugged - except those devices that are connected to the UPS, which are just switched off.
I have not experienced any problems when powering back on.
Regarding companies that leave PCs on overnight - I think that the realities of cost savings will make themselves felt soon enough, if not already.
Wake-on-LAN is good enough now to permit admin tasks to be done overnight.
SD