How much value does the financial industry create?

Everyone knows that the finance industry has grown in America. In 1980, finance took home about five percent of all the income in America; in 2007, about eight percent. This has led many people to question whether all this activity is worth what we pay for it; in other words, how much of the increase in finance-industry GDP is actually value added, and how much is "rent" extracted from the rest of the economy?