With just the default settings, cups-pdf is not working. Kernel complains:
I have PDF directory and even set the permissions to 0777 (755 used to work with karmic koala). How do I fix it?
Dec 28 11:56:13 <hostname> kernel: [22362.501505] type=1400 audit(1293537373.392:2429): apparmor="DENIED" operation="mknod" parent=16861 profile="/usr/lib/cups/backend/cups-pdf" name="<home_dir>/PDF/<job_name>.pdf" pid=16862 comm="cp" requested_mask="c" denied_mask="c" fsuid=<uid> ouid=<uid>
There are also plenty of other warnings with evince thumbnailer for some reason, perhaps unrelated, but an indication that apparmour is out of step with the other applications/packages even in default setup.