That wikipedia article references lots of diverse uses of the Lorentz Force and Hall Effect, including moving sea water with magnets ala Red October and Ion drives, which are indeed high efficiency/low thrust. The MHD drives in 2300 are not 'BS' in that the concept is sound, the numbers are definitely heavily tweaked in order to increase fuel efficiency greatly.
MHD as a power source
As far as I understand it, MHD power plants in 2300 create a plasma by burning liquid hydrogen and oxygen, pushing the resulting plasma into the turbine where it creates electricity just like a regular generator, except that the plasma takes the place of the spinning coils in the regular generator. So you'd need to ignite the fuel, to start the process, just like you need a spark to start an internal combustion engine, thereafter the turbine will produce net power. The violence of igniting the hydrogen and oxygen is enough of a jet to create and move the plasma in the first place - this is what real rockets today use as reaction mass after all.
A lot of traditional power stations are considering using MHD turbines to produce extra electricity from the high temperature gasses they produce from coal, oil or other fuels. The RPG Albedo also used MHD turbines to generate electricity by passing the exhaust from their fusion rockets through an MHD turbine on the way out of the exhaust.
So MHD turbines are conceptually real power generation sources, which current technology is just about on the cusp of deploying usefully for power generation.
MHD Thrusters as rockets
In 2300 AD, the game posits simply sticking a hole in one end of an MHD Tubine to let the plasma escape as a rocket exhaust (I imagine they'd have a magnetic nozzle to focus the plasma into a high-pressure jet). You would also add the electrical power the MHD generates, or some portion of it, to heat the plasma to increase the energy of the rocket exhaust. In this case, you'd have essentially the same engine that modern rockets use – a jet of hydrogen burned in liquid oxygen, with lots of electrical power added to it).
There's no reason this wouldn't work either – Ignite liguid hydrogen in oxygen, push it through an MHD turbine where it generates a current as it passes through, use that electricity to heat the exhaust again just before it passes through nozzle as a rocket exhaust producing thrust.
You can see a discussion of this in the 2300 AD technical architecture series here [http://www.caco.demon.co.uk/2300ad/Locomotion.html] – this article concludes that 2300 MHD thrusters are in the ball-park of projected advanced rocket performance, they are just much more fuel efficient, a deliberate sin all drives in traveller seem to be guilty of, so that the players aren't squeezed into a capsule at the end of a flying fuel tank.
