Most of the business of the Supreme Court is not about interpreting the Constitution.

It is about interpreting laws made by Congress. Why would they even need interpreting? In part because they are made of words, and people do not agree on what words mean, especially when one meaning causes a company to lose millions and another for them to make millions. The other thing is that Congress often has trouble passing laws, and ends up passing them knowing there are ambiguities. It's the only way to get them passed and a controversy out of Congress' hair, so they can go back to getting re-elected. They expect the SCOTUS to fill in the blanks. Just like singers covering a popular song put their own gloss on it.

In filling in the 'spaces' in Congress's laws it is unavoidable that the SCOTUS—and the thirteen courts of appeal below it—makes policy. As an example, what does a Justice do when the patent law grants an inventor a monopoly on his or her invention, and the anti-trust laws try to bust up monopolies? Well, you try to balance inventor rights against those of customers and other manufacturers. That makes policy. There are also cases when what is needed is to figure out how to mold the words of a law to carry out Congress' purpose. Only 100 senators and 435 Reps did not have a common purpose. Again, the courts of appeal and the SCOUTS make policy.

In maybe 10% of its cases the SCOTUS has to make something of the Constitution. That short body of words is very pithy and usually does not do much more than write in brushstrokes. It is not possible to "just interpret" the document, because there is not so much document there. Therefore, there are two schools of thought. "Strict constructionists" try to figure out more than 200 years later what the drafters had in mind. (Sometimes they are called "textualists" and strict construction" is taken to mean the same as "conservative.") Of course, there were 39 signers, and they were not of one mind. The other school, which has only pejorative names, believes in trying to interpret the scanty words in modern contexts. Who, for example, would seriously claim that words carried over the internet, or even by phone or telegram, are not covered by the First Amendment protection of freedom of speech and press? Still, neither was even dreamed of when it was approved.

In short, most of what you will hear the next few months as the Senate debates Judge Sotomayor's nomination will be political malarkey from both sides. Remember that a person's political philosophy before taking a Supreme Court robe is often no good predictor of what is to come.