Oh...and: I had a minute yesterday to spend with a student's Intuos tablet. With this plugged in and the Cintiq removed, Photoshop returned to performing with its usual responsiveness. Like I said, though, I only had a minute or so to make a series of rapid brush strokes with a default airbrush, though. I didn't have time to try out anything more robust.
I do not have an Intuos, so I can't utilize this option. And, (I may be a spoiled brat saying this) the Cintiq has become a part of my workflow—especially in that it enables me to skip the stage of sketching on paper altogether.