I have tried to put my first app onto extras-devel.
This is mostly a specific implementation of Saslers countdown timer customised to allow me to count my Physio Exercise Reps (I had an ACL reconstruction on my left knee last Friday).
The code now deploys to extras-devel thanks to following this guide (http://talk.maemo.org/showthread.php?t=39962) and my app appears in the app manager list, but when I install it nothing happens. The appears appears in the "Utilities" categories and is called "Exercise Rep Counter". There should be a sitrep.png file installed to "/usr/share/icons/hicolor/64x64/apps" (I think) and the app to "/usr/bin" (again I think).
Update: I just searched the N900 and there are sitrep files in the following folder and it's subfolders - /home/builder2/maemo-fremantle-armel-extras-devel/work/sitrep-0.4/