Because today's new houses are built to allow less air infiltration than older homes, mold growth has become a concern. Properly installed roofing and tile, ventilation fans in bathrooms and kitchens, and pans under washers are all good ways to avoid water infiltration and mold growth in your home.
For more on mold and mildew, consider:
DIY Mold Removal
Radio: Mold Removal
How To: Prevent Mold and Mildew