I am the co-founder of Open Rev. (www.openrev.org), a platform where researchers can collaboratively annotate research publications and scientific books. I am a physicist and we designed our platform such that scientists can explain complex scientific contexts to each other (latex, markdown, image support).

I presume that there will be little “where is this reference from” but more “what does this word mean” (for example look at all these acronyms in biology and chemistry papers).

Third kind of annotations is simply posting links to good references. From tests in Physics classes it turns out this is what students did and liked a lot. Sometimes its just damn hard to find a good explanation or image of a physical concept.

That brings me to my last group of annotations: Explanations. That is the rephrasing of the scientific language that is sometimes written truly encrypted. We also anticipate people to improve the scientific content by suggestions new solutions, highlight flaws, post missing derivations, etc. This is likely the hardest annotation form, since it requires "academic rigour" as some of you have noted. And this is what we are shooting for.