In the example at left, I show the simplest use case, where you want to link a term to its entry in Wikipedia. What I like most about this is how easy it is to add more information to your pages without having to do editing of the original content. I could see this kind of functionality being very useful for altering original content if these kinds of widgets were available within the rich text editors themselves. It's very nicely implemented, and if set to only fire on click (rather than on hover), this is nowhere near as intrusive to me as ad-supported services like Snap.
Content editors who don't want to know anything about HTML need simple interactions like this to make their work quicker and easier. I imagine that this kind of interaction could be scoped within a specific body of content as well, e.g. to easily create links within a wiki. CMS vendors take notice.