What matters more so than how much weight you've got hanging on the wall, is how far out from the wall it's hanging. I'm thinking that you're talking about 1 foot deep shelving, or similar. In that case, just make sure you anchor into the studs and you'll be fine. That's not a major lateral force; it's all right up against the wall. If you want 4 feet deep shelves with the weight at the edge of the shelf, that's a different story.