[Zatko]

Robby - for those blue leggedds to "strip your rock surgically clean," I would imagine you'd need quite a large number of them.

I've heard 1 crab per gallon of volume in the tank. I'd imagine it would have to be a tank loaded with live rock as well. Them actually causing any kind of damage to the rock (i.e. killing off sponges, coral gametes..) is pretty negligible. Your live rock should contain tons of little creatures, more than an ample supply of food for your corals, fish, and crabs.

Don't fret, these little guys may look like they are doing some sort of damage, but those are diligently working the algae that you cannot really see. If you are looking for more of a cleanup crew for detritus and excess food, go for the scarlet reef/red hermit crabs. They are a little bigger, but have a lot more color, and tend to be a little more active in my opinion.

One more thing - putting your hands in the tank consistently and moving things around is more of problem then those crabs. And if you are really concerned about them stealing food from corals and whatnot, use a turkey baster or a low flow power head and blow your rocks causing a small kick up of whatever is on the rock. A few benefits of this is corals feeding off the critters you've just thrown into the current, and also, corraline algae will grow where the sediment that you blew off once was. So more desirable algae and an easy/cheap way to feed your corals. But please do not over do this. Don't blow off every rock and expect a feeding frenzy (I would advise blowing off most of your rock prior to a water change, though). More than likely you will cause the corals to recede and possibly affect the oxygen exchange in your fishes gills.

Anyway, I went off on a tangent there. Hope I answered something.