staplerer

I remember hearing that the signal from pulsars can be used as an interstellar positioning system in much the same way as GPS satellites are used on earth. Pulsars don't transmit their position like GPS satellites, so how would this work? Also, what type of accuracy could be achieved?

I know that "dark matter" cannot be observed directly, but are there any astronomy experiments being run or conceived to try to observe it indirectly?