What multimedia should do

Here's a rollover idea that so clearly adds to the understanding of the text that it's hard not to be excited about it -- so I'll stick with the enthusiasm. Slate carries the text of Obama's acceptance speech. As you mouseover the highlighted areas, a text box appears to the right of the copy. Inside, it contains explication or context for the highlighted material. So smart. It doesn't hinder the reading through distraction or tempt the reader to leave the page; what it does is return the reader to the reading feeling smarter, more informed.