A standard drywall saw is a crude not very sharp saw that you punch through the wall and cut with. There are new drywall saws beginning to show up in stores that have the sharp Japanese style teeth that cut in both the push and pull directions and with a very sharp point to the saw. This Shark Tooth saw is a beauty to cut into the wall with, but I can't find the manufacturer anymore. However, with the growing popularity of the Japanese style teeth I am sure you will see more of this type of drywall saw in the near future.
You can of course cut out drywall with a jig saw. It is efficient but very dusty with the drywall dust pulling back onto the surface and the saw blowing it all around.
The real professional cut out tool is a specialized little router, made just for cutting holes in drywall and panel boards, cleanly and quickly. You can get special "down spiral" blades for this saw that will force all the dust into the hollow wall, making it easy to watch what you are doing.
There is a video clip on cutting holes in drywall in the Learning Curve Tab above, or just click here.