Other than hurricane induced power outages, my little 250W PE plate amp has been left on 24/7 for the last about four years or so with no problems.

It has always switched from standby to on without a glitch(I keep it located out of the sub cabinet where only I can see it cause I'm constantly curious about whether it happens to be "on" at the moment or not...ya can't usually tell unless there's a major blast or something!!)