It looks like they've sped up forward/back, folded in some of the extension features and fixed the awful autoupdate. The coolest new thing to me is the newfangled SVG/Canvascape support. Here's a couple of neat demos.
http://www.abrahamjoffe.com.au/ben/canvascape/
http://www.croczilla.com/svg/samples/svgtetris/svgtetris.svg
Canvas in particular will be used for some way cool things. Safari also finally fixed their broken canvas in the latest update (you'd THINK they'd get it right since they introduced it, but apparently not).
