Same issue as Remoran; I'm also running Diablo.
I installed xournal on 10 Oct 2008 and it was one of my favorite apps. I used it not only for drawing, but for note-taking and marking-up a pdf document for revision.
I upgraded on 27 Nov 2008 and now the app sometimes doesn't open (though you can see it in the task manager). When it does, the icons don't work, so for example after clicking on the eraser, it still draws as a pen. The icons have changed too, critically with the "undo" missing (you can undo from the pull-down menu). The application is now next to useless. Other than by install date, I can't even tell you what version I'm running, because "help" no longer works at all.
Please, please either sort this out or tell us how to go back to the previous version. Thank you!

I remind all of you that there is NO DIABLO UPDATE of Xournal. The latest, working, version is this one.
If you've update Xournal to the "alpha" Diablo version, remove it, disable Maemo Extras Devel (for Diablo) and re-install this version.
Thank you.