If you want to know the weather the day you were born...
I came across a cool search engine, but not a search engine really - it's more of a computational knowledge engine. You can type in any calculation and it will solve it for you. Also it will display all things related.
For instance, if you type in "tan(x)" it will show you the graph of tan(x), the expansion, different formulas / identities, properties, etc. If you type in sin(60) it will find the exact value for you, but also give you a decimal approximation, the right triangle with the representation. You can also do harder expressions and more complex functions, and it will do integrals, derivatives, etc.
But it's not only good for math. It also is great for science. For instance, you want to balance a chemical equation, but you don't know how. So you type in: C2H6+O2 --> H2O+CO2. The Wolfram|Alpha engine does it for you:
Not only that, but it gives you the thermodynamic properties of each of the reactants and products, the equilibrium constant, the structure diagrams of each of the reactants and products, etc. Awesome!
Or, let's say you are on a diet, and you are counting calories. Packaged foods have serving sizes and the different caloric intake. However what about a carrot. What if you ate a carrot, and you wanted to know how many calories you consumed. Did you know that one carrot has about 13.5 calories and 66mg of fat? I never thought that a carrot would have any fat. What a cool tool!
I was playing around with it all day. Trying to figure out how it works, and what it understands. But I was sold when I typed in my birthday and the city I was born. It gave me lots of stats about that day, including the weather. I found out that I was actually born on a Friday, and that the day was foggy and overcast (100% cloud cover) with an average temperature of 4C. I must have been the only ray of sunshine for my mom that day :)
The Wolfram|Alpha engine of course does other useful things such as physics, engineering, finance, geography, etc. Endless possibilities!!!
When you try it out, you'll have so much fun with it. But eventually, I see this engine as a great tool for all my students, teachers, friends, and anybody that wants to know anything to do with numbers, stats, comparisons, etc. It's going to be my primary source of info for sure. We are slowly but surely getting away from textbooks and reference books. This is the next step. I can see it growing as fast as Google has.