Almost always, though, it seems to happen at the line whenever a stop light turns green - where, perhaps, there might be some oil on the road. Also, it seems to happen more frequently during the start of my drive - when, perhaps, the tires are still cold and not as "sticky."
The conclusion that I'm drawing is this: the car is able to detect an imperceptible loss of traction and react within milliseconds - so sensitive and so quick that I was thinking there was a bug, since I could not perceive ANY traction issues that would warrant the ESP activating. To put that in perspective, a "blink of an eye" is about 150~200 milliseconds, by the way.
I'm not sure if I'm used to clunky and slow older types of control systems, but it's kind of weird. In a way, I want that physical feeling of a tiny bit of slip before the system activates (as a cue that it's happening); but on the other hand, it's nice to trust that the car is actually taking care of things for me - and doing it well. Just one more old habit to break, I suppose!