My house is only 4 years old and many, many tiles on the shower wall and around the tub have hairline cracks. Where the long crack lines (some are 38 in long) cross the tiles, the grouts in between are still good (no crack).
I posted this in the foundation forum, thinking that since the house sits on expansive soil (Northern California) the cracks must be from the movement. But none of my neighbors on this street have cracks like this. We all have the same PT slabs foundation. Thanks!