Hi mace,
I believe that long-term deterioration due to heat build-up when you leave equipment powered on outweighs any effects caused by the on/off power surge when you turn equipment on or off. For the casual use most consumers make of A/V gear, I believe turning it off extends service life.
I can speak with some authority here: I'm old! And I have some solid-state gear that dates back 25 years that still works perfectly. In an age of diminishing fossil fuel supplies, it also strikes me as egregiously wasteful to leave equipment powered on.
Historically, this trend migrated from professional recording studio and broadcast practices, where equipment used to be left on because it was in more or less constant use. And in the vacuum-tube era, leaving equipment on usually meant more consistent performance because tube performance drifts and takes a while to settle down when they are fired up from a cold state.
And what is it these days with outboard hard drives that have no on/off switches? I thought I'd lose data if I unplugged my Maxtor, but it's fine. It drove me crazy when I'd walk by the thing and hear it whirring away at night in my home office. So I unplug it when I'm not in my office.
Regards,
