Glad to read in the blog post that the new viewer will be faster and will abandon Flash. Maybe Flash was the reason my cursor would often slow or freeze when mousing over the body area of the Interactive Image Viewer... it's like it would get stuck in the body section. I also had trouble where I would use common scroll movements in my browser and it would interpret them incorrectly, doing things I hadn't intended like zooming in and out or shifting to another part of the census image. So I often had to switch back to the basic viewer.
In theory I like the advanced features... it is very convenient in censuses to have the relevant fields highlighted and indexed and be able to see birth years at a glance.