Well, the Popular Mechanics website states that you actually can stop a car at full throttle in gear by pushing as hard as poss on the brake. The brakes are more powerfull than the engine, Sounds right to me unless your brakes are knackered.
This seems to make sense as cars are alpine tested with a load trailer down a very long downhill alpine pass with the handbrake on...repeatedly, till the brakes boil and then some. The cars brakes have to work in that situation otherwise you cant legally sell them.
Engine off, the brakes will work but with no servo assist (so the brake pedal will be harder) but also most cars will loose their power assisted steering in this situation. Handbarke will always work as its cable actualted. IIRC electronic handbrakes are on an emergency system so should be independant of the ignition.
If you're in a manual car the first best course of action is to stand on both the clutch and brake pedals as you retain brake servo, power steering etc. Had this happen to me a few years back in a car where the floormat moved forwards and got stuck over the accelerator...scary but easy to stop the car provided you stay calm.
Autos are a different issue but you still have some manual control over the gearbox. You should be able to at least change down, not sure about getting the car into Neutral under full load though but I cant believe that you cant...hmmm, can you crash change it?. If you cant it seems the best option there is to cut the ignition, stand on the brakes with both feet and pray.
Oddly enough a lot of uncontrolled acceleration incidents in the UK are due to people mistaking the accelerator for the brake, then pressing harder when they start going faster...
A 2009 model Lexus would not have an old style planetary-auto (i.e. non electronically controlled) however.
