I've been trying to figure out why exactly the streamgraph was such a big hit to the mass audience. The Byron/Wattenberg paper puts it pretty clearly (and was a pretty interesting read). It pretty much came down to a visualization that didn't look statistical. Streamgraphs have an organic feel to them, and it drew people in - like the data had life.
That's what excites me most about data visualization - the blend of statistics and design. Statistics is really good at finding interesting things in data and design is really good at evoking emotion. Put the two together, and you've got some excellent viz. I just wish there was more blending going on.