Here's a chart of the S&P 500 over the past year or so. (The Dow Jones 30 would show the same pattern.) The black bars indicate the month or so during which earnings are reported -- January, April, July and October.
Click on the graphic for a larger image
January 2010 was not a great month -- stocks fell about four percent. But in the other earnings months, the index rose one percent, seven percent, and four percent respectively (total 12 percent, and a net of eight percent counting January).
Extending the pattern to include the month prior to earnings, where there has been a consistent move up as well, earnings season gains this year have been about 20 percent.
Meanwhile, net-net from December 31, 2009 through November 17 the index is up just under six percent. The micro of positive earnings news giveth, while the downside of the world macroeconomy taketh away.