Went to Sacramento to pick up some real live rock today from an aquarium shop that I knew would have some. As can be seen from the picture on the right I bought 5 pieces. I most likely won't leave them in the positions that they are currently in, but wanted to get them into the tank ASAP given the trip out of water from the fish shop. The piece on the far right had some dead material that needed brushing off, but other than that these rocks have been fairly well cured. I use the term cured in the sense that live rock that comes from the ocean usually has various plants and animals attached to them. Some of these aren't able to make the trip from ocean to the aquarium shop, and die in-transit. So the rock needs to be brushed off of dead matter, and spend some time recovering in a tub with good water movement and a protein skimmer. More dead material sloughs off, the water is changed, and slowly the rock begins to come back to life. The rock I bought today has already been through most of this process, so there shouldn't be too much concern about huge ammonia spikes in the tank due to rotting matter.
The reason for using live rock, is that it is rich in microbes, and algae that help make a reef system sustainable. It is a necessary component to a saltwater tank that is going to have corals and other invertebrate life. So in this case, I am using a few pieces of live rock to 'seed' my homemade rock. In time, my homemade will become alive with new generations of microbes, algae, and the two should be indistinguishable in outward appearance. Time will tell.