Couple of things... First, if you're not getting trailing-throttle-oversteer, you're not driving the car hard enough through the corner! Ideally, what you want to do is hit corner entry, hard, and still under braking to set up a little trail-brake rotation. Dynamically, this is happening because you've transferred the weight forward (braking) and to the outside (turn-in), pulling the weight off the rear. The rear tires, with reduced load from the transfer, simply can't grip and begin to slide, so the car starts to rotate. Once you have the rotation started, you control the yaw by getting off the brake and into the gas, which pulls the weight rearward, increasing the traction to the rear. Note however, that this implies that you have gotten the front to bite and turn in! Once you're back on the gas, you can control the rotation (yaw) with the throttle. More gas means more rear bite and less rotation, less gas means less rear bite and more rotation.
The whole point of this rotation business is to get slip angle on the tires. Tires provide maximum traction in a certain range of slip... A slight wheel-spin will provide more traction on launch than dead-hooking, in the same way that a slight amount of lock-up will provide more traction under braking than NO slipping. If it's visible, you've gone a touch too far, but a slight amount is still critical for maximizing what the tire can do. For street tires, a slip angle somewhere between 8* and 16* will probably give you the most traction the tire can produce, but you need to get it in that range, and that means cornering load. To get that load for a given corner, you have a fairly narrow range of speed that you have to be in, plus the chassis setup to balance the car out front and rear in those load conditions.
Not bagging on you, just hoping to push you a little harder through the corners. If you're going through a corner where the throttle doesn't do anything to orient the car, you're simply not going fast enough! In practice, you want to feel the car start to spin at or just after turn-in, catch it with the throttle, and then push the car (with progressively more and more throttle) through the corner with the tail hanging out slightly until track-out where you unwind the wheel and the rear end drops back in line with the front. I only use opposite lock when I've overdone the throttle thing and the car is rotating more DESPITE the gas! When you dial in opposite lock, you take the chassis out of "set," then roll it back in again when you unwind the lock, none of which allows maximum weight transfer to the outside tires. That means less grip, and that means less speed. That's that whole "smooth is fast" thing.
Applied theory:
1: turn-in and start the rotation.
2: catch the rotation with the throttle, incidentally causing the car to start accelerating!
3: keep rolling into the throttle as hard as you can, holding the car's attitude. If possible, go to WOT at or slightly before apex. Note my hand position... With the induced rotation plus the acceleration, the car is effectively sliding through the corner, so I can unwind the wheel a lot sooner. Since there is no more steering drag (differing slip angles front and rear), I'm accelerating harder, sooner, and that translates to more exit speed, which is what it's all about.
4: start to unwind the wheel, and feed it more gas (if any's available). Note how tight the car is to the inside edge of the track, and that while the wheels are straight (check hand position), the car is still sliding away from the center of the corner, so it's still heading for the proper track-out point. In the case of this particular corner, the track-out point is actually mid-track to set up for a gentle left-hander that follows. As you can see from the roll angle, the car is still set on the suspension, despite having the wheel unwound.
5: Unwind completely, foot to the floor, on the way to track-out. The suspension is now back to un-set, I haven't touched the wheel, and the car is still drifting away from apex and heading towards track-out. I was pulling a pretty consistent 1.2-1.3G in this corner, with turn-in around 75mph, and my Traqmate showed a max-Q of around 1.5G.
Maybe Sam can chime in for autocross-specific comments, but that's my take based on vehicle dynamics. It doesn't matter whether you're cornering at 30mph or 130mph, it's still all about managing weight, and making it work for you.
