i used to have a krell cd player, and while it had an on/off switch, it was really an on/standby switch. what i did not like was that krell components tend to consume a fair amount of power while in standby. when the cd player was in standby it was warm. i currently have a wadia cd player and while it has an on/off switch it is located in the rear of the unit because the intention is that the unit should be left on all the time. the wadia cd player is fairly cool, which suggests to me that it is not consuming much power; if it were warm, i would definitely reach in the back to turn it off when i wasn't using it.
03-01-11: Mitch2
The manufacturers of my SS disc player and SS preamps say to leave them on all the time (one of the preamps doesn't even have an on/off switch).
my attitude about it is that if the power dissipation is like that of a night light, i won't make such a big deal over leaving it on; after all, displays on microwaves and ovens consume energy; but when the energy consumption is enough to light a room, then that's a bit too much to leave such a component on 24/7.
one of my criticisms of the audiophile biz is that it seems to often promote profligate waste for little (or effectively no) benefit...