Ok this isn't really a major issue, but if there's a way around it then I'd be interested.
At the moment I'm not really using an external HD for any purpose, but still have it plugged in, with the software set to put it into sleep mode after 3 minutes if it's not being used. It's actually noisier than my PC so it's something I would rather not have humming away if possible.
I have noticed that when I shut down when the HD is not in sleep mode, it shuts down pretty much instantaneously. With the HD in sleep mode, we're talking about a minute.
What could be the cause of this? The PC is trying to shut down, and can't see the HD because it's having a nap? Would be nice to know.