Just played with a FS100 at the booth at NAB. The build quality was very comparable to my EX1. I was worried after reading a review trashing the build quality, and it's about what you can expect for the price.

The boxy form factor is actually ok to operate cradled down in your hands, not looking through the viewfinder. You would definitely want a shoulder rig to operate in a more ENG way.

Overall I was pretty impressed, again considering it's price...