> The main difference between Genius-style annotation and code comments, which I think is important to note (and valuable) is that code comments annotate a point or position in the source, while genius annotations are referring to a span or range in the source.

I don't think that's necessarily true; code comments very often refer to a range in the source. Because code is generally designed to be accessed as linear text without hyperlinking facilities, the identification of the range is usually something that the reader has to interpret by applying (sometimes language specific) conventions relating to code formatting, indentation, and the precise placement of comments, and there are a limited set of kinds of spans that conventions cover (e.g., a span that starts in one block but extends to include the following part of the containing block doesn't have a good layout convention to indicate that a comment goes with it.)

Genius-style annotations, because they aren't limited to conventions that work in a strict linear text medium, can easily refer to arbitrary spans of content.

Well, I think the idea is sound. I'm even into Hip-Hop/Rap, so I should like them.

Unfortunately the user interface is a world of pain. It's unusable. It's worse than quora. Good idea, but the execution needs work.

Agreed. Just separating concept from implementation.