A couple of random thoughts to share on various responses in this thread:
* Some throttle position sensors (TPS's) use a dual potentiometer where the slopes are inverted relative to each other. The ECU understands this and correlates the detected throttle position based on the (intentionally dissimilar) values it reads from the two pots. This prevents a short across the two pots from being missed. If EITHER pot's value doesn't correlate with the other, the ECU (at least) gives a warning and (at worst) goes into "limp mode" where RPM's are severely limited - basically enough that you're not stranded but not fast enough to put you in too much danger since as far as the ECU is concerned, you no longer have actual control of the engine.
* The terms "leading throttle" and "lagging throttle" have a couple of definitions depending upon context. This thread has used one, but the more common I hear is the relationship between the engine loading and the throttle position. To illustrate an extreme example of "throttle lag", imagine a moving car where you've completely released the throttle but left the clutch engaged. The engine compression is now acting as a brake, slowing the car, so the throttle is "lagging" behind what is necessary to match the losses and maintain speed. On the other end, a "leading throttle" is enough throttle that the engine, while under load, is causing the vehicle to accelerate (and thus the engine RPM's are climbing). If you think about it, lagging vs. leading will engage/load opposite faces of the gear teeth in the drivetrain. Somewhere in the middle is the sweet spot where the engine just matches the drivetrain... and the gears sort of "float" mid-tooth with little sustained loading in either direction.
* "Lag" has other uses too. For example, "turbo lag" refers to the delay between increased power demand from an engine and the spinup of an exhaust-driven turbocharger to provide increased ("boosted") intake air pressure. This is very common on modern diesel engines, virtually all of which have turbos (and those turbos recover ~50% of otherwise lost energy out the tailpipe, one reason diesels are so much more efficient). For those engines where such lag is intolerable, superchargers are the answer; they are driven directly from the crankshaft and so immediately track the engine's behavior. The tradeoff is sustained efficiency... the supercharger consumes some power even when not required and fully bypassed, whereas a turbocharger can always recover some otherwise lost power and the ECU knows how to accommodate that thanks to the countless sensors measuring everything. Hence turbochargers are better for long term sustained applications (over the road trucking, marine, etc.) while superchargers prevail for high performance engines requiring rapid acceleration (racing cars, racing boats).
Opinion time: I deplore the drive-by-wire, integrated design of today's cars. As much as I'm fully immersed in modern technology, there are times when it's possible to overdo it. I do not want a steering wheel position sensor driving a linear positioner to steer the front wheels... it's far less reliable than a simple shaft driving a rack-and-pinion. The latter will fail gracefully and allow me to control the car to a safe stop, but a failure of almost any component in an electronic steering system means you no longer control your vehicle. There is no graceful degradation.
Granted, some things like fuel injection (and its associated ECU and sensors) are definitely worth it. But they don't threaten the ultimate safety of the car. If the engine stops, you can still coast to a safe stop most of the time. But pushbutton "shifters" or (heaven help us) KNOBS that in reality just control a bunch of transmission solenoids? Seriously, I rented a pickup truck from Hertz recently and its automatic transmission was controlled by a rotary KNOB. I sat there dumbfounded for a while, utterly speechless at the concept of replacing a very straightforward shaft or cable system with switches, wires, and solenoids. That is NOT progress, people. Not everything on the planet needs to help you play "astronaut". Some things should just work nice and simple.
Perhaps the best example of this over-technology is touchscreens in cars. Seriously? Instead of a nice tactile rotating temperature control that I can operate by feel while keeping my eyes on the road, you want me to be a distracted driver while I look over at the screen, work my way through several menu layers, finally find the temperature controls, and then carefully align my finger with the up or down arrow? This is no different than using a smartphone while driving, which is illegal in a growing number of jurisdictions. I'm waiting for the lawsuit where someone claims "distracted driving" from a touchscreen led to an accident that killed someone. They don't want ME on that jury, because my 100% objective opinion as an Engineer is that touchscreens make cars more dangerous, period, full stop.
Technology is wonderful. But it's not a universal solution for all situations. Sometimes an array of sensors, harnesses, motors, and solenoids just isn't better than a shaft or a cable. If you want to play "Space Shuttle Pilot" play a video game at home.
/rant