When driving on the track, or when driving in a "spirited" manner in the hills, I disengage the TCS and the ABS as well. I do this to get a little wheelspin and drift through the corners and to modulate the brakes more. The TCS and ABS are both excellent systems, but they interfere with the smoothness that I want when driving hard. During everyday driving I leave them both engaged.
BTW, you can turn these systms off by lifting the handbrake lever one click and driving for about 20 or 30 seconds. Disable lights will appear on your dash indicating that both systems have been temporarily disengaged.
[This message has been edited by ChopsJazz (edited 21 July 2000).]