I use OneNote extensively, on multiple devices, on a daily basis. I have never used pen input. I know many OneNote users. None use pen input.

Because it seems like the developer never used it, otherwise he would not write thank Microsoft "For making terrible products" in the credits.

Exactly. OneNote is the only piece of software I've used that does stylus-based notetaking right. And Microsoft has been supporting this stuff all the way along, which means notes you take today won't be obsolete tomorrow.