So, extrapolating from what Issac said, the Island will be the right healing energy for some people, Rose and Locke for example, but not everyone, Sawyer certainly didn't benefit from it.

It will be interesting to see if Locke's injury does heal faster than it normally should.

I took that to mean the island is kinda like one big giant magnetic bracelet that prevents joint pain.

Maybe this is why many of the other islanders also do not seem to be as interested in trying to leave ... maybe they all have been experiencing some kinda of "cure."

well it most definitely didnt heal the federal marshall!

It's apparent that the island has some kind of secret power source, probably magnetic in origin, that can heal pre-existing physical conditions, like Locke's paralysis, Jin's sterility, Rose's cancer, etc. I think this is what Isaac was alluding to in the scene with Rose. Even though he said he couldn't help her, he could see in "reading" her that there was a place that could. It's also quite possible that Isaac worked for Dharma, and was really working to steer Rose and Bernard toward the island. And in the same way it can heal pre-existing conditions, the island can also accelerate the healing process for someone who is injured there, like Sawyer, Locke, and Henry. But if one's wounds are more fatal, like Edward, Boone and Shannon, there's not quite enough power to heal someone physically. If one's condition is mental, like Hurley's, it may have no power to heal physically either. Instead, maybe it projects a kind of mental imagery, like Hurley seeing Dave, Kate seeing the horse, and Jack seeing his dad, as a way to treat their respective mental illnesses. Or, it could work in the opposite by creating hallucinations to further drive someone mad. As usual, lot's of exciting possibilities and no real answers yet!

I thought I heard Isaac mention "white" energy. What if the island is over a spot of contrasting energy? What if there are centers of different "colors" of energy around the world and different people react or respond differently to each location; this way, Locke and Rose and Jin respond to the island's energy source but Sawyer and others don't. And what if Dharma has tried to "harness" (the word Isaac used) all these energy sources with sometimes unexpected consequences?