Today I was thinking...that while waiting for me to finish the Xournal port, you guys should have something to do with the beta released so far :)
To help came the folks at Internet Tablet School who made a nice tutorial (Nokia N800 & N810: Take notes and doodle with Xournal) on some of the features you can find in Xournal (even though they missed the most important feature for me: Annotate PDF).
Simply jump here and take a look at it!