I have a Wacom Intuos 5 and I'd like to use the touch interface to pan horizontally. But so far, I can only pan vertically. I can press shift at achieve horizontal panning, but that's not intuitive.

Does anyone know if it's possible to do what I want?

Hello:
You don't say what configurations tried, so:
In Inkscape 0.48 there is only 1 GUI interface that I know to config an input device:
Menu> File> Input Devices
Also, In Menu>File> Inkscape Preferences there are options for scrolling and Mouse.

However, There is possible that some options of your hardware aren't recognized by Inkscape. I tell you from user to user.

Please, check here:
https://bugs.launchpad.net/inkscape

OK, I've figured it out. I gave up on trying to use the touch interface (which I think only maps to equivalent mouse actions) to scroll horizontally. I just set the action of a button on my pen to do pan/scroll - way more precise and easier to use than touch.