Sweet, I didn't know that SRV used one from time to time. I actually knew Eric Johnson used one, it just slipped my mind.
Last night I was actually playing around with volume swells with my chorus pedal on. I played whole bar chords with the volume all the way off, then slowly roll it up on the beat (like I learned in your Baroque and Roll). It almost sounds like some kind of keyboard effect!
I feel like I should call these "chorus swells."