I have another thought about live rock that I haven't seen mentioned elsewhere: When calculating the amount to use, consider that the more you use, the more water you will displace in your aquarium. In other words, say you have a 30 gal aquarium, and you add 30-45 lbs of live rock, displacing maybe 10 gal of water. Now you have 20 gallons of water that you're actually working with, making your tank that much more vulnerable to fluctuations. And now that you have that much less water volume, you re-calculate that you should be using only 20-30 lbs of rock! I think the 1-1.5 lb/gal rule should just be used as a guideline, and could even be decreased for smaller tank sizes.
Just a thought.