Email marketers take heed-- email remains the most popular online activity in the nation, according to a survey released by Mediamark Research and Intelligence. The survey found that almost three-quarters (74.2%) of all U.S. adults use email, an increase of 5.2% from Fall 2007. The "Fall 2008 Survey of the American Consumer " also revealed that 46.0% of respondents obtained news online; 37.2% m...