What are they really seeing with body scanners?

If you've flown anywhere in the last few years chances are you've had a few runs into a TSA body scanner for security.  They tell you to raise your hands up, stand still and then you're cleared to fly.  But who's seeing what behind the scenes?  

For the most part they get a grainy black and white image that'd be hard for even the most horny TSA staff member to get too excited about, but yes, they can see the general outline of your body.   Mostly they show if you have any hidden weapons.  Going through airport security is not a who's hotter naked contest;  it's a who's carrying the most dangerous items contest.  

I don't have a problem with the scans myself, it's better to be safe (and show off naked) than to be sorry.  That's just my take.