I've gotten a bit more committed to SVN for the new input devices dialog. It does tracking of buttons and axes now, with different graphics to show ones that have been seen, ones that have not, and ones that are currently active.
There are two main benefits right off the bat (aside from the gratuitous "oooh, pretty lights" factor). First is that it allows a simple way to determine what inputs any given device really has, as opposed to what is reported to GTK+. For example, my tablet's pen says it can handle 7 macros, but it only has 3 buttons. And I've seen that although the driver reports six axes, I only get data on five (aka there is one 'dead' input axis).
The second main functionality is to allow a user to see which physical parts of his devices are hooked up to what. For example, an Intuos3 tablet has buttons and touch strips on the tablet itself, but it may not be immediately obvious how those are configured. Under Linux, I see those strips as the x-tilt and y-tilt axes. Also using the visual feedback it is easy to see which buttons have which numbers.
Then below I'm using progress bars to show the current values of the axes, so it's easy to get an idea of how those values range on different physical changes. I still need to add some visual feedback for those that have no bounds, but those are usually the ones mapped to x and y, so are already being used for positioning.
Now the next thing is to get some feedback on how this works for other people. That will also help for the "Configuration" tab which will allow setting of things such as screen versus window mode, button actions, etc. Those may change with the user's current task, but the hardware usually will stay in one (or a very few) combination.