If you're remodeling or adding a bathroom, use cement board as an underlayment. A bit of hardened mortar is sandwiched between two layers of fiberglass sheets. It cuts and trims like sheet rock, but it provides a waterproof layer under wall or floor tile. To attach it, drill a pilot hole first, then use galvanized drywall screws.
For more on building materials, consider:
Deconstructing Engineered Wood
Concrete and Cement: A Case of Mistaken Identities
10 Ways to Use Glass Block in Your Home Design