I've only driven 2 gokarts where i had to use the brake, usually its just foot to the floor and hold it there lol.

 

Actually come to think of it I use my left foot for braking a lot when I'm driving a stick or a semi auto car in a Auto X type of event. The brakes lock up the fronts harder than the rear, the E brake locks up only the rear so when I'm doing an auto X course I take a warm up lap determining when to use normal brakes & and when to use the E brake. In the M5 last year I posted a 59.99 sec lap time in an auto X event and the 2nd place guy was at 1:07 with a Ferrari something. So yes I do use my left foot for braking just not in daily driving type of situation.