So I had to uninstall the ppa version of Xournal and build from source (with a modification). And now .xoj files open automatically with KDE's archive manager Ark, and are identified as being of type ...
I just installed Kubuntu 12.04 beta 1. Both Rekong and Firefox don't know how to "Open Containing Folder" for downloaded items. They also don't know how open the item itself. (I'll give the specific ...