I still have a problem, that the generated svgs are bugged though. The box is strange and the plot doesn't appear.
Seeing the same thing here (gnuplot 4.2 and inkscape 0.46). It seems that playing around with the opacity of the objects will make them appear (in black and white). They are 100% opaque, but if you select everything, drop to 99 and then back to 100, the plots and axes appear.
This renders perfectly in Firefox (3.0.7).