Cycling is the process of building up bacterial populations in the bio-filter. In a modern saltwater aquarium, the live rock is the bio-filter, and the bacteria are already on it when you buy it. So you put the rock in the tank and call the "cycle" done.
That being said, the main thing that allows the live rock to function well as a bio-filter is the availability of oxygen in the water. High levels of oxygen saturation come from the output of the protein skimmer.
In fact, it's pretty much the invention and popularity of good protein skimmers that allows us to use live rock and get rid of the wet-dry.
So if you're using a wet-dry, another source of bio-filtration, or an alternative source of oxygenation, then you'll be fine without the skimmer. Otherwise, I would have it running when I added the rock. Without a good oxygen source you may get a decline in bacteria population and then go through another cycle when you add the skimmer and teh first waste-producing life.
[ February 19, 2002: Message edited by: MattM ]</p>
