I would argue that whilst pen usage might have been rare a decade ago, almost everything supports it these days, as its been baked into win32 api since XP. I mean every app written in WPF, winforms, all of windows, every mechanical cad package ive ever used, all work fine. The exception to this is custom controls that directly interpret mouse-move events and don't follow current guidance.
I was hoping that someone had found a workaround for the problem, altium may use mouse and 3d navigator, but that's pretty useless on a slate tablet pc.
EDIT: the problem is when the targeting crosshair is displayed when placing a part, wire or bus, when the pen is outside of the canvas control, the crosshair moves around the edge of canvas as expected, and clicks place parts. But moving across canvas / clicking on it doesn't update the crosshair as expected. The rest of the UI works fine. That said I have an older version, so if someone has experience with latest release can you let me know.