I've deliberately provoked VSC on many occasions (vacant parking lots in the snow, etc) but only had it activate on its own once.
It was a gradual curve, extending into shade that had created some black ice. Fortunately I was going slowly, but I wasn't paying especially close attention and didn't know about the ice. Somewhere near the middle of the curve I was just starting to notice that I was getting a little more turn than I was intending with the steering wheel. Just at this moment the computer figured out that I was getting oversteer, beeped at me, braked one or both wheels on one side, and I was back exactly on track in a fraction of a second.
The stability/traction control system in the 4Runner is pretty conservative, but I haven't found too much to gripe about on the roads. Offroad is another world, and I don't have much experience with the 4Runner there yet.