If you are using OneNote 2003 on a UMPC make sure that you download and install this update:

Update for OneNote 2003 (KB917148)

As the text on the site says:

Microsoft has released an update for Microsoft Office OneNote 2003. When you write with the pen on some touch screen devices, the pen stroke is only visible as long as the pen is touching the screen. This update resolves that issue.

Just something I wanted to pass on to you all..if you are running OneNote 2007 on a UMPC this is already fixed in that version.