yep thats what ive herd aswell. personally im not a fan of idling, even when the car is cold in the mornings, just start it, get comfy, find a good radio station and go, usualy just keep it under 3000rpms until it gets to operating temp.
but you only left it on over night once, not like you do it every week, i wouldnt worry about it too much, maybe check/clean ur plugs...