If you're wondering how much energy is consumed by your electronics, a base model kill-a-watt for about $30 will show you watts and cumulative watt-hours. It's a fantastic tool that pays for itself besides giving an eye-opening, interesting experience. You'd be surprised at the things in your house consuming electricity 24/7. Almost everything in my house is either on power strip surge protectors or just unplugged.
For sure! I found a pioneer amp that sucked 200W sitting there doing nothing. No increase when volume was turned up either. I compared to an older 1970s model that started at 3w and went up from there with the volume.
That's a difference between class A and B amplifiers. The former draw the same power all the time but are very linear, the latter don't consume much power at idle in exchange for small harmonic distortion.