I have experienced so many instances when the ESP is working in the background and the light doesn't even flash to signify!
Try accelerating hard in first gear, and changing into second. If your gearchange is fast and admittedly not smooth with the clutch, the power just doesn't come, and it feels like a 1.2 accelerating! But no ESP light flashing as per normal. If you try this with ESP off, then the car just rockets!! With no wheelspin inbetween changes either - therefore asking the question why ESP felt the need to come on in the first place!
I also find that the car feels so much more eager to turn into corners with ESP off. It definitely feels like a completely different car - in a good way
Don't get me wrong, I am not promoting constant ESP-off driving, however as R32UK said if the road conditions allow it, then turn it off just for a couple of minutes and just give it a try - you can always turn it back on again!