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.

Found a very informative thread by Buehl. Stone Information and Advice So looks like cracked stone is a no-no Also the saleswoman showed their countertop in the showroom and said that a seam will be visible and will be felt with a finger. I don't know how to measure the seam, but it seemed too big. 1/4 mm maybe? She was a very good saleswoman, Didnt hurry us or push us towards a particular slab, was helpful. The price is great too. But now I am not sure if should continue with them ..

I think the biggest issue here is that there are two different lots and one is more desirable than the other. We didn't ask our granite yard to move the 6 slabs in the stack on their assurance that pense's "sliced bread" thing applied to this particular granite, all in the same lot. They did go out with a marker and wrote our name along the edge of the first two themselves when we called in our confirmation of which stone we'd decided on (took 2 samples home). Having said that though, I think weissman makes an excellent point about slabs that have big movement in them. One way or the other, it's a good idea to see your name in indelible marker on the edge of specific slabs.

PPF: All materials have a coefficient of linear thermal expansion. Coefficient of linear thermal expansion for concrete is roughly the same as for iron which is why it (rebar) works well with concrete. Expansion/contraction is significant for long linear surfaces such as the large concrete slab with the crack OPs thread. Though there is a much more to material science, especially concrete and types of concrete, hopefully the following excerpt provides an adequate explanation. THERMAL EXPANSION AND CONTRACTION Materials expand or contract when subjected to changes in temperature. Most materials expand when they are heated, and contract when they are cooled. When free to deform, concrete will expand or contract due to fluctuations in temperature. The size of the concrete structure whether it is a bridge, a highway, or a building does not make it immune to the effects of temperature. The expansion and contraction with changes in temperature occur regardless 0of the structure’s cross-sectional area. Concrete expands slightly as temperature rises and contracts as temperature falls. Temperature changes may be caused by environmental conditions or by cement hydration (the exothermic chemical process in which the cement reacts with the water in a mixture of concrete to create the calcium silicate hydrate binder and other compounds). An average value for the coefficient of thermal expansion of concrete is about 10 millionths per degree Celsius (10x10-6/C), although values ranging from 7 to 12 millionths per degree Celsius have been observed. This amounts to a length change of 1.7 centimeters for every 30.5 meters of concrete subjected to a rise or fall of 38 degrees Celsius. Thermal expansion and contraction of concrete varies primarily with aggregate type (shale, limestone, siliceous gravel, granite), cementitious material content, water cement ratio, temperature range, concrete age, and ambient relative humidity. Of these factors, aggregate type has the greatest influence on the expansion and contraction of concrete. Severe problems develop in massive structures where heat cannot be dissipated. Thermal contraction on the concrete’s surface without a corresponding change in its interior temperature will cause a thermal differential and potentially lead to cracking. Temperature changes that result in shortening will crack concrete members that are held in place or restrained by another part of the structure, internal reinforcement or by the ground. Forexample, a long restrained concrete section is allowed to drop in temperature. As the temperature drops, the concrete tends to shorten, but cannot as it is restrained along its base length. This causes the concrete to be stressed, and eventually crack. Joints are the most effective way to control cracking. If a sizable section of concrete is not provided with properly spaced joints to accommodate temperature movement, the concrete will crack in a regular pattern related to the temperature and restraint directory. Control joints are grooved, formed, or sawed into sidewalks, driveways, pavements, floors, and walls so that cracking will occur in these joints rather than in a random manner. Contraction joints provide for movement in the plane of a slab or wall, and induce cracking caused by thermal shrinkage at preselected locations. One of the most economical methods for making a contraction joint is by simply sawing a continuous cut in the top of the slab with a masonry saw.