People would indeed be thrown off if the Earth spun about 17 times faster. (In that case, the day would be only 84.7 minutes long). At the present rate of its rotation also there is an effect due to centrifugal force
, but even the inhabitants at the equator – where Earth’s spin is the fastest – don’t notice it. It does reduce the pull of gravity, but by only one part in 189. The pull of gravity is further reduced for another reason: The equator is about 20 kilometers farther from the center of the Earth than the poles are, and gravity always decreases with distance from the core. The Earth is shaped somewhat like a slightly squeezed-in sphere such as orange, bulging at the equator.
At the poles, which are closer to the core and where there is no centrifugal force from rotation, the pull of gravity is 1/189 stronger than it is at the equator. An object weighing 189 kilograms at the equator would weigh 190 at the poles.