On the bright side, they were awful at judging value. For example: they emptied out my Tootsie roll bank (had ~$15 worth of coins) but left my small (and growing) collection of Sega Genesis games sitting right next to the TV they took. Also, they left my expensive graphing calculator and Oakley sunglasses (which were right next to my Tootsie Roll bank).
It's usually someone you know, from what I hear, but I have had less than 5 non-family members over to my place, ever, and my family absolutely didn't do it. The criminal went to my back porch, climbed onto the roof of my garage, jumped/grabbed onto the railing of my balcony, climbed over it (bringing with them a small decorative shovel I have outside that came with the house), cut through the screen door to unlock/open it, smashed the glass door with the shovel which only sort of worked, then smashed the door in breaking the frame of the door itself. This motherfucker really wanted the ~$500 worth of stuff he stole.