I would suggest adding a feature Inkscape has, which is that a single middle click zooms in. This is not at the detriment of panning, since the mouse/pen (I use a Wacom tablet) doesn't move. Right now middle click doesn't do anything so I don't think it should be a problem.

Another awesome and related Inkscape zooming feature is that Shift+middle click shifts to window zooming. But with the added bonus that you don't lose the tool you're in. Try it out on Inkscape if I'm not clear!

Cheers,
JFL