I got a 100S this week and am very happy so far. The differences I know of are an external RF antenna, a 20gb bigger (320gb) hard drive, and it runs very cool due its noisy fan. I came from an AT&T Dish Homezone 622HZ box that would fry eggs so I had some extra cooling in my bag of tricks.
I added a 12v pancake fan pushing air into the right side vents and a PCI Card Slot fan pulling air out of the left side vents. The volts on both are cut to 6v making them silent. They are so effective the on board noisy fan never comes on. Temps are in the low 90's. The Dish box needed to sit on a laptop cooler along with four other PC fans.
Operationally the box is flawless. I did the IAMANEDGECUTTER trick and the box FF's like my old TiVo. FF followed by Play backs up a bit leaving you right where you want to be, i.e, the end of the commercial. Pretty cool.
I am very happy so far and glad to be back with D*.