The Guardian features a great in depth article about Wolfram Alpha and Stephen Wolfram, the man behind it. Wolfram Alpha, as he puts it, is a computational knowledge engine. Wolfram Alpha was not designed as a search engine but as a "answer machine". But how can a machine produce useful answers - that is, when user don't just type in keywords to search for? It means that a computer has to understand natural language. Well, the technology is still work in progress. As expected, Wolfram Alpha is works best with questions in mathematics in science. You can read the whole article here.