For a while I have been either not LaTeXing a lot, or not using AucTeX frequently. Strange indeed! But in July, while in Göttingen I wrote part of some lecture notes of one of the courses. And again, used auctex-preview in emacs to find errors in what I was writing.
I can't even tell how wonderful it is, to share the source with the images with the formulas. An image is worth more than a googol words.