This excerpt taken from the NDAQ 10-K filed Feb 27, 2009.
Current economic conditions could adversely affect our market data revenues.
Market data revenues may be significantly affected by the global economic and credit markets crises. Professional subscriptions to our market data are at risk due to the extensive layoffs and staff reductions announced throughout the financial services industry. As these reductions occur, we may see significant reductions in our professional user revenue from our market data. While volatility in the markets may help the non-professional segment of our market data subscribers, the global loss of wealth and the steep decline in markets may cause a reduction in the number of non-professional investors who leave their investments in the market. Therefore, we may see a declining population of non-professional investors, which could result in lower non-professional subscriptions to our market data.