This is supposed to be operational in April (2011). I can see it practicing from my window. The train is two cars long. I have heard it will depart every 20 minutes. I haven't heard when it will cease operations at night. It will make a stop at Gimhae Airport, so it will be great for vacations.
Basically it goes from Gimhae - DaeJo station (Busan Subway Line 3) - Airport - SaSang (Busan Subway Line 2).
More info here: http://en.wikipedia.org/wiki/Busan-Gimhae_Light_Rail_Transit