Zemanta is an interesting idea. It works as a Firefox add-on that regularly analyze the text you are writing and fetch related images and links. When trying in WordPress 2.3, the add-on integrates into the writing page tighly. The suggestions, on the other hand, could be improved.
I think the suggested images are relevant, but the links are not. It looks like they try to identify important nouns and give you "encyclopedic" or defining links. When people blogs, there is usally a story being told, and the links do not help much. If they leverage on technorati or Google blogsearch, it could become a powerful tool, since they have got the UI down quite neatly.
The easiest way to try Zemanta out is pasting some text into their demo page and click go.