It all depends on the nature of the cracks. If a crack follows a panel joint it is probably due to poor installation or use of insufficiently dry framing. Look for screw pops to support this assumption. Cracks in a ceiling are usually due to these factors or unusually high humidity and if the cracks are at the ceiling-to-wall joint it can be because the installer screwed the ceiling edges to the framing instead of allowing the wall board to support them. If a crack is vertical at a door/window corner then the installer probably put a joint there which, of course, he shouldn't have. If a crack is diagonal across a panel it is most likely due to foundation settlement. Settlement should produce cracks in the foundation as well so it is usually not difficult to see. It is possible that the model unit was built to meet a tight deadline and the drywall joints were taped with a fast drying "setting type" compound and painted the same day. If you are really worried you should photograph the cracks and post them here or get a structural engineer or architect to visit the site and report back to you.

The first thing you have to do is eliminate the stress that caused the cracking, then you have to repair the cracks then you can look into a decorative overlay.

We hired a contractor to reface our entire concrete porch, including the flush brick trim and steps, in Pennsylavania Gray Flagstone. Assuming you don't want to do anything that drastic---you might be able to use concrete patch on the crack then repaint as brickeyee suggested. There are specific paint formulas just for concrete.

A properly repaired crack will not be any threat to crack again in a horizontal use situation as long as it's supported properly and that support doesn't shift over time---and it's not an inherently weak stone that is prone to cracking as some of the pricier already mesh reinforced and resined ones are. It will still be visible as a vein in the granite but should be mostly smooth to the touch, similar to a fissure. I wouldn't personally have any fears about installing such a stone in my own kitchen as long as the fabricator was well experienced with epoxy repairs. If you are uncertain, let them repair the slab now before fabrication and see what you think about how it looks. And thoroughly inspect the stone for mesh and resin reinforcing as your choice may be one of the ones that is fragile.