Tim, thanks for the reminder about the WD40. I was told that by my machine technician also. His other no-no was to toss out the compressed air cannisters. All the air does is push the lint and dust deeper into the mechanics of the machine.
I'm really not sure about the question of leaving a machine on or off. I turn mine off whenever I'm not going to sew for a reasonable amount of time. 15 minutes or so, but it varies depending on the distraction!
I did run one idea past my machine tech and he liked it so much he's passing it along. Here in California we have a lot of electric outages, especially in the hot weather. Any electrical equipment that's plugged in, whether it's left running or not, can be shorted out by the jolt of the power coming back on. Every machine should have it's own surge protector if it's left plugged in all the time. A very small investment can save a very expensive machine!
You're right about the lightning strike, tho. Surge protector would most likely be the first thing fried!!! If anybody's looking for me, I'll be up on the roof installing a lightening rod.....