Lin Wang finished fine tuning the Windows Journal Importer tool and here it is. Just like it's name says, this tool will let you import your Windows Journal files from your tablet into OneNote. It's not strictly a OneNote addin - it installs into the start menu and runs externally to OneNote.
Setup is "the usual"- make sure OneNote is not running, runs as admin, install for everyone. (Update: this is now in the readme file.)
When you open the program, you will see this
Obviously, browse to the location of your Journal files in the top box (the default on my computer was Documents\Notes), and specify where you want the new notebook the program will create in the bottom.
The interesting item here is the link to install the "Microsoft Windows Journal Reader Supplemental Component for the Windows XP Tablet PC Edition Development Kit 1.7." OK, it's a long name. The development kit has some files needed for the converter to work, and it is a relatively small download (1.3 MB).
After that is done, click Import and the Journal files will get imported with each journal file getting its own section, with each page of data getting its own page as well.
(update) Get it as an attachment below my signature at the end of this article.
Most of the code for this has already been published on MSDN at http://msdn2.microsoft.com/en-us/library/ms812502.aspx if you want to see how it's done. Thanks Casey.
Questions, comments, concerns and criticisms always welcome,