IDEA (Institute for Dynamic Educational Advancement) has conducted a survey about Factors That Improve Online Experiences which you might possibly find interesting & helpful.
The report emphasizes facts like the importance of visual design & ease of use. And also, it points out interesting information like “designers being overly optimistic about visitors’ ability to maintain orientation”.
You can download the full report as a PDF file or read the shorter executive summary.
Here is the methodology behind the survey.