Because the pen records my writing and audio as needed, I find a subtle pressure to write legibly, organize my thoughts, and speaker clearly when recorded.
I'm also enjoying OneNote. Even without a pen and tablet, who would have thought it cool be so awesome. Do people use "awesome" anymore? How about stinky cool?
Anyways, we're heading for a show down because both tools overlap in responsibilities.
I think the pen will win for meetings and capturing, organizing, and sharing thoughts "in the wild" away from a computer; while the software will be my super-duper-uper-smoocher research tool and educational assistant.
Speaking of tools, check out Craig Roth's post about matching collaboration tool to the right scenario.