We've been observing more spoken language with Ben. It's a really slow progress, and I think we can consider "no" crossed off the list - he'll use it to announce displeasure, defiance and sometimes to answer questions in the negative.
But "yes" (and "yeah") are newer. At night when getting him ready for bed I'll use iPrompts Pro to offer him the choice of crib or bed and Verbal Me Free for yes/no questions like "Do you want guys (stuff animals) in bed with you?" and then "Do you want your monkey/puppy/Mickey/etc." He'll usually press yes or no. Not always with care and sometimes just a swipe at the screen but if I guide his hand, he'll indicate what he wants.
Today there were two instances where he answered me affirmatively verbally. I can't remember one of them, but the other was pretty cool: I had offered him a pair of gray socks and a pair of blue socks. He took the gray pair and I confirmed "Ok, gray socks." As I went to put the blue ones away he said "Other" and I said, "Oh, you want the blue socks" and he responded "yeah."
It may not seem like much if you're parenting a typically-developing child, but for Ben, this is a huge step and exciting for us.