Hey, I've left the house before with the amp on, a guitar plugged in and the damn thing sitting there ringing feedback (just a little - not out of control feedback or anything) I'm just glad that I didn't burn the house down.
I have an old Peavey VT Classic that I left on overnight back in like 2002, it blew a fuse and wouldn't turn on afterwards. It sat unused until I got it fixed about a year ago.