I worked in Comet for a 2 years at the store in Aberdeen when i was an Engineering student. The general advise from the manufacturers on their shop display recomendations was to leave them on all the time - especially the projection units and plasmas to avoid thermal cycling. CRT's were ok as in standby the filaments are kept warm and LCD's don't have any problems.
The ones on the shop floor only went off at night for fire risk and the electricity bill which was several MWh per month!!
