Beany : one of the problem of SVG, is that it's a retained-mode (in contrast to Canvas - immediate-mode).
And, when you are starting to have a lot of vectors elements onscreen, browsers are going to stutter. The Flash VM handle this differently (and was built from the ground up to deal with vectors). However, browser are optimized for raster.
Although I'm the developper of the SVG plugin, I don't think a whole game made only with SVG can be good (performance wise). You need to use SVG for effects and GUI, for example, in that context.
I'm planning to add more functionnalities to the plugin, anyway.