In general we tip 10% of the bill in restaurants, 15% if the service was really good. You should tip more in places frequented by americans, like Cancun or Los Cabos. In more traditional places like San Luis Potosi or Queretaro the expected tip is usually smaller.

Like the article said, you don't tip the cab drivers, and don't expect an envelope for the maid in not-so-expensive hotels. You can however leave your tip under the pillow (and so you assure it's really the maid and not her supervisor who takes the tip).