This morning's breakfast experiment: the peanut butter smoothie. Lacking in any frozen fruit besides bananas, and reasoning that since PB shakes are good, this might be, I threw some yogurt, a frozen banana, a couple tablespoons of PB, and a bit of sugar into the blender.
Verdict? Not as thick as smoothies with more fruit. Not bad. Not what my taste buds expect when thinking "smoothie". Would eat again, in a pinch.