Those motors do look interesting.
The main thing I usually hear about hub motors for use in a car are questions about "sprung weight" since the weight of the motor is on the road instead of in the engine compartment, held up by the suspension.
Pretty cool that you can get ones that already have brake discs on them. Range of voltage isn't bad either, they have 48-96V versions.
My other concern is that they say "brushless DC". I know brushless controllers start to get a little on the fancy side (price!) and you would need one per wheel, so two controllers at a minimum. I am not sure how turns would effect the power/signal, etc going to the wheels either.
I would think that you could have one potentiometer sending the same signal to both motors, as long as everything is identical - exact same motor with same settings.
I really neat advantage of hub motors is that you don't need any room under the hood for the motor. Put two of these on the back of a Metro or Festiva, and you got a hot hybrid!!!