I would love to be able to use Protovis but as an SVG-only toolkit it is not very practical if you have to provide a good experience to MSIE 7 & 8 users - see http://multimedia.journalism.berkeley.edu/tutorials/protovis...

(Yeah, I know, if they wanted a good experience why would they use IE7? But I think we have to live with IE8 for a good while.)