We started this as a way to experiment with the Flex framework, and Flash / AJAX integration, and have been really happy with the results. By leveraging Flash and AJAX together, we can take advantage of the strengths of both Flash/ Flex (interactivity, ease of development, experience) and HTML (easy layout and formatting, displaying large amount of text based data), and ultimately provide an over all better user experience. Plus, if the user is using a browser that does not support AJAX, you can still view the data within the charting app.
Anyways, we are going to try to make another post with more detailed technical info on how the reports are put together.
You can view all of the reports here.
Btw, these reports are a lot of fun to make (we have two more about ready to launch), so if you have a suggestion for a specific report, please send it email@example.com.