It's actually quite safe, really, and it's where you install stuff and know "holy crap, this app is horribly broken and unmaintained, time to post on tmo and restore".

SAFE AND RECOMMENDED THINGS TO INSTALL OFF EXTRAS-DEVEL:
fapman (hildon app manager sucks so bad for daily package management)
openmediaplayer semi-monthlies
semi-latest version kernel-power (repo management is broken, by the time it gets pushed to devel pali has a newer one on the usual place)
pierogi
h-e-n
busybox-power
GNU Core Utilities
tracker-cfg
bluemaemo
mbarcode
mypaint
frontview
easy-debian