How does the remote control on the 9398 4X4 Crawler work?
You'll want to read the TechnicBricks review of that set, which is quite detailed.

In short, there are two new motor types; one of which is a servo motor used to control the direction. As the remote used is the usual on/off one, it means you'll be able to steer right or left, but with no granularity (you can also go straight ahead, of course). The other motor is a regular one, but again the lack of granularity on the remote means you can't modulate the speed of the car.

TechnicBricks also has an article dedicated to the two new motors themselves.

Having never really used remote controlled cars, I can't say how it compares to the real stuff. I suppose the lack of speed regulation can be a problem, but you should be able to build a better remote using the IR Speed Remote Control .

Edit: according to LEGO the new motors will not be available separately before march 2013, which I suppose means they will be available separately.