Both of my boys love to examine things.  See how they tick.  Emerson, our youngest, started this fascination young.  He's 13 months now, but has been poring over objects (toys, bath soap dispensers, his brother's toys, etc.) since birth.  At least, that's what it seems like.  He pulls stuff apart methodically, tries to see how it works, then tries to put it back together.

I've noticed lately in my usability testing that people get extremely frustrated when they can't quite see what the computer is doing.  Which is often.  They can't look behind the screen, see gears moving, and understand if their work is going to save, or if they actually emailed their friend about that great movie. 

I always understood that we as designers need to remanufacture all of those mechanisms for feedback and affordance, but my last test still surprised me.  We are building a video tutorial with pretty high financial rewards for completing it.  The stakes are high for the users of the site.  Consequently, we are saving their progress for them every 5 seconds on our servers. Even if there is a cataclysmic failure of their computer (ex: a whale swallows it), their work is safe.

However, half of the users were very hesitant to log out halfway through the session (simulating an emergency in their life that they had to attend to) without saving their work.  "Where's the save button? I see the logout button, but where's the save button?" They sat and would not continue on their own without knowing that their work would be saved.

So we're putting in a save button.  It won't really do anything that the system isn't doing already. But, extrapolating from our results (which is always dangerous!), we are probably saving our client thousands (if not millions) of dollars in customer support calls.

Best. Save. Button. Ever.