Do computerized clinical decision support systems (CDSSs) make a difference? An article published in the Journal of the American Medical Association (JAMA) titled Effects of Computerized Clinical Decision Support Systems on Practitioner Performance and Patient Outcomes concluded that "Many CDSSs improve practitioner performance. To date, the effects on patient outcomes remain understudied and, when studied, inconsistent."
This article is available for free download from the JAMA website. Definitely more work is needed to determine whether or not eHealth systems have a measurable impact on patient outcomes.