Wolfram Alpha is a new web service. It is not a regular search engine like Google, but rather it is a computational knowledge engine. It's makers say it is not meant to be a regular web search engine and is not in competition with search engines like Google and Yahoo.
It doesn't find other web sites for you, it actually will do math computations and aggregate data for you. For example, I entered in New York, New York and it came back with New York City's population, area, location, and more. You can enter dates, towns, math formulas, stock symbols, and more and Wolfram Alpha will calculate the math and gather all kinds of data for you.
I entered my birthdate and got back holiday observances, notable events, time difference from today, daylight information, moon phase, and more.
Entering physics concepts and formulas got me a huge amount of data and allowed me to solve a complex formula.
It is an interesting concept. I think it will be a very useful educational tool, as it can help students find certain data and information more readily than a standard web search.