as far as i remember antimatter is not 100% efficient. its only 50% as the other 50% gets carried away by nuetrinos. and fission would be a much cheaper alternative wihout the undesirable nuclear waste from fusion.
the most technical thing i've done w/ antimater is on futurama when that penguin thing craps its antimatter and its really really heavy cause its all dense and stuff
and I will admit I had to see if antimatter and dark matter were different things because I thought "Hmm, maybe it's just a different term for the same thing" because I didn't know what antimatter was. I did know what dark matter was though and I knew it was what that little creature pooped out.
dark matter is so called becasue no-one know what it is basically some astro-physicists calculated that there should be a lot more mass in the universe than is visible in the night sky... hence "Dark" matter.
mrcoffee half said it. dark matter is mostly theoretical based on the fact that there apparently should be more matter in the universe. i think it is also partly based on the way light refracts around matter and the fact they have observed some such effects where there is no visible matter :/
If you want to know more about this, look up dark matter, dark energy, and super string theory/symetry. Thats one way they explaing the increase in the speed of galactic expansion.