One of the major concerns with running a leaked version of OS 5.0 has been
the fact most RIM designed applications were not yet compatible with OS 5.0.
FaceBook is of course one such application that until earlier tonight was
among the non working applications, but RIM has rather quietly updated
FaceBook to version 1.6.0.22 which does indeed make it compatible at this
time. So if you have been running any of the leaked version 5.0 operating
systems and been missing FaceBook you can grab the updated version and be
back in business.

http://mobile.blackberry.com