Do you always keep the Amplifier powered on

All due respect to Schubert, but you don't turn off your refrigerator when you leave the house. I have been an appliance service technician for thirty six years and have seen appliances that came very close to starting a fire but haven't.
I would not be apprehensive of leaving the amp on. Whatever you are comfortable with.

Yes, I do leave it turned on (tube amps, no). I read somewhere that turning your amp on and off is actually harder on the equipment than just leaving it on all the time. I'm sure there are other items around the house that we leave on all the time. Clocks come to mind...

It's kind of funny to hear you guys break down the cost ($20-$30 per year) when you probably have $500 speaker cables... Yes, I'd like a super sized big mac combo with a diet coke please, I'm watching my weight ;)

Hi Mtrot, what amp breaker are you useing on your krell 400cx?, do you have a dedicated line for your amp?, I can help you here if you answer, may be able to get your amp to run alot cooler and smoother, more dynamic, speed, etc...

Almarg's post of 12-17 is spot-on:
"The OP might consider asking the manufacturer how much AC current or power the specific model draws at idle...I suspect that the sonic benefit of leaving it on all the time will be minimal."
In fact I was considering the Moon NEO 330 amplifier (250 wpc into 4 ohms) and asked exactly that. It draws 40W in standby, as pointed out in Almarg's post - not a true standby. For me, and given the recent 40% increase in electric costs in Boston, this is too much, economically and ecologically. We light our kitchen with less than 40W using LED's. To their credit Simaudio acknowledes this and says they are working on a true soft-start.
It is easy to look up the temp curves for power bipolar transistors. The effects are very small for normal room temps. So, unless your amp runs hot and with minimal or no feedback or active bias, any effect would be minimal.

Went with ATI - a true standby/soft-start with active bias. The newer thermal track transistors (also used by McIntosh in the MC452 and other models) would also render this question essentially moot.

I leave my yba pre and 600 power amp on 24\7 the instruction manual recommends this.It runs cool anyway even after a long listening session.