I never use auto unless it's the only option outside of manual, i usually work a scale that uses less fan at lower temps and only increases in reaction to temp increase, like i guess a lot of other people do, no point in wasting effort when you arent running hot
typically my sapphire fan runs at 7% when i'm just on and not doing anything particularly loadsome, but then the temps are usually anything from 24-33 C idle.
when playing Metro or Deus Ex it gets up to 48 C on load, and using the scale it only goes up as far as 45% fan usage - based on a 100% Fan @ 70 C