Where can I find information regarding national intake levels of sugar and caloric sweeteners?
FNIC has a variety of information regarding sugar and sweeteners at Food Composition > Nutritive and Nonnutritive Sweeteners.
A table from What We Eat in America (PDF | 62KB) by NHANES shows the mean daily intake per individual of total sugars, including all sugars in foods and beverages, reported from 2009-2010.
In addition, Sugar and Sweeteners Outlook (PDF | 1.30MB) from the USDA's ERS shows useful pie charts and graphs that illustrate the average daily per capita calories from sugar and sweeteners from 1985 until 2010. In particular, see pages 11-12. For example, Figure E shows that the average daily intake of added sugar and sweeteners in the U.S. in 2010 was 379 calories, or 15% of the daily calories consumed.