I replaced all my rock with marco rock last summer and while I'm just now getting some color on the rocks, it's done wonderfully. The rock I got was large pieces and it was nice being able to sit down with it and build the structure on cardboard prior to getting it in the water. I had run the tank fallow due to marine velvet and just pulled the old rock out and pretty much put the new in after rinsing.
If I remember right, Marc is running a shipping special right now as well.