Do you leave your components on 24/7?

As was pointed out above, the answer is component specific. My ARC 150.2 SS amp is designed to be left on 24/7, and in fact ARC comments that if turned off, it can take up to a week to get back to full "musicality" once it is turned back on. My CDP stays on stand-by when not in use. But my ARC tube preamp is turned off after use, and only turned on when I'm going to listen; ARC's comment is that leaving it on continuously would merely wear out the tubes prematurely.

Hello Mitch2. You should try Sanders Sound Systems Magtech amplifier. It is recommended that it stay on all the time. Look at the review in the February 2011 issue of the Absolute Sound. You have 30 days to audition the amp in your own system and the amp has a lifetime warranty. It will deliver 500 watts RMS into 8 ohms and 900 watts into 4 ohms. It will truly make your speakers sing. Check out all the info on Sanders Sound Systems website. I use the Magtech to drive a pair of Duntech Sovereigns.

I experimented with my modest SS system, left it on for couple of days and in another case didn't leave anything on.
Well, it didn't really sound good cold. However, there was no or little difference in sound between being on for two days and being on for two/three hours. So I usually keep it on on weekends and turn it on on weekdays in the evening.
Another point might be that you don't want your equipment to be on and even plugged in when there is a storm. And one can never predict the weather.

I leave everything on standby that is solid state, but not the pure class A Threshold T-200 - it takes about 20 minutes to warm up and start to sound good. The outboard power supply of my Threshold DAC-2 runs extremely hot, but I leave it on anyway since the manual recommends it - and there is a noticeable difference after it's been on for about 72 hours.

Never. I turn everything off.