We use both at work (along with Pixate depending on the situation) and based on conversations I had today with our IX guys the main difference seems to be that

We use both at work (along with Pixate depending on the situation) and based on conversations I had today with our IX guys the main difference seems to be that Form makes it easy to mirror on your phone and actually play with the interactions, where as you can't do that with Quartz/Origami (the playing with interactions). I'm sure there are other differences as well (I'll see if one of our guys will come and comment here), but at the end of the day they both seem to have their place depending on the situation. I definitely agree it's 100x better than PSD/static mocks however and I hope Google continues to put resources into this.