Can you leave class D amps on and not ever turn them off?

Guidocorona, it couldn't hurt anything to try on occasions as long as you power everything down first. You could actually leave the system unplugged for a few minutes then plug back in. This is a tweak that won't cost you anything.

George can you give us a couple of examples of the ones that go up in smoke?

Ones I remember
Panasonic PVR's, dvd/cd players, Samsung, Panasonic TV's,  2 x Velodyne CHT15 subs, 1 x Alesis 620, 1 x Nuforce 8 monoblock, 1x Halcro DM68 that had to be shipped back to manufacture. 1x Behringer B2031A, 2 x Behringer active xovers. 
These are ones that were left on or in standby.

Many others were blown and popped their fuse but didn't fry up. 
Countless smp battery chargers, some of them liked to fry with much crackle and big smoke.

Cheers George

I hope when their switching power supplies blow they won't destroy the speakers, but I suppose that is why they are protected by a fuse.

Grannyring, give it a try. Afterwards of course you will still have to wait for it to reach its optimum operating temperature for best sound but it will provide better overall sonics for a while. Let us know later if this made a difference.

George,

You mention NuForce 8 monoblocks as having gone up in smoke.
Would you suspect the Nuforce 9's as having  the same problem?