What are your thoughts on realistic returns from the S & P 500?

I have always just played it safe and calculated all potential returns at 8%. Dave Ramsey seems to think 10-12% which is theoretically correct based on history but I don't believe he is telling the whole story with those numbers. After inflation, fees, and taxes can you still be at 9% per year long term? Or, can you explain to me what numbers are realistic and how you calculated them?
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Tags: Finance and Investment Source Type: forums