In any non-trivial SVG document I've viewed, the default viewport chosen by Safari is far smaller than is useful. For example, in the following SVG document, the default viewport shows nothing but white space, and even zooming out 10 times showed nothing.
WebKit should try to pick a viewport based on the overall size of the SVG document. A fairly simple way would be to default to displaying the entire document in the viewport, even this simple change would be far more useful than the current default.
It's not the default viewport that is the issue here, the SVG content has this:
<svg width="124422pt" height="143420pt"
this is telling webkit the image size, which is huge.
Also, much of the graphics in the file is positioned outside that anyway - see all the negative y coordinates.
Huh, I didn't actually inspect the contents of this file (since it's so huge; I picked it because it was the same file I used to file another bug), but speaking purely as a user and not as someone who knows anything at all about SVG, most non-trivial SVG documents I've encountered defaulted to a useless viewport. Unfortunately I don't have any others on-hand, as I encounter SVG documents so rarely.
Crazy large SVG :-) The bug is fixed in trunk, you'll now see scrollbars to navigate around...