So, today at my PT appointment, we measured my range of motion and compared the numbers with what they'd been on my first visit:
lifting arm straight up in front of me: range of motion increased from 130 degrees to 160 degrees
lifting arm straight up to the side: range of motion increased from 110 degrees to 160 degrees
holding elbow at side and rotating lower arm outward: range of motion increased from 30 degrees to 60 degrees
My PT doesn't record a numerical value for the "reaching up to scratch between your shoulderblades" motion, but he considers me now able to reach my "mid-back" rather than just "lower back".
I've still got some way to go, but that's a very nice rate of improvement!
As my reward, I get a new batch of exercises to add to the ones I'm already doing. Wheeee!