On a recent trip to my lfs (the only one in the area which carries a decent amount of saltwater supplies and fish) I inquired as to whether they would be selling live rock anytime soon. The owner said that "Live rock is a great way to kill a tank". I put two large peices in along with some regular rocks before cycling the tank, and they are still in there. They seemed to help, and other than the possibilty of pests hitching a ride on the rock (which is easily remedied by curing), are there any other serious consequences? The rock I have in the tank has not caused any problems, so I am wondering if this guy is just 

