The fastest computer, being built by IBM today will be able to do 1 quadrillion calculations per second (1,000 trillion), which is a petaflop (1015). It's supposed to cost $110 million dollars to make over three years and will be located at Los Alamos National Laboratory. Now before we get a bunch of "$110 million for a computer!" posts, please consider the following;
Exxon will have a profit of more than 100 billion over the next three years. $110 million represents 0.1% of their profit.
The Iraq War over the past three years has cost more than 300 billion dollars. $110 million represents 0.03% of that amount.
The US has a 8.5 trillion dollar debt. Last year the US paid 400 billion in interest. $110 million represents 0.025% of the US national debt interest paid every year.
NASA plans to put a perminent base on the moon. The Estimated cost is 230 billion dollars. $110 million represents 0.05%
Yikes.
Anyway, supercomputers are used for a number of things including the aerodynamics of potato chips to predicting the weather to engineering smart materials.
http://edition.cnn.com/2006/TECH/12/05/supercomputers/