Yahoo tells us that we SHALL NOT...
Use the Yahoo! APIs to operate nuclear facilities, life support, or other mission critical application where human life or property may be at stake. You understand that the Yahoo! APIs are not designed for such purposes and that their failure in such cases could lead to death, personal injury, or severe property or environmental damage for which Yahoo! is not responsible;
Upon additional reflection these seem like a good ideas. Yahoo appears to be watching out for those of us that might tend towards these types of uses. They also forbid using Yahoo APIs to traffic in body parts or materials urging acts of hacking.