We just released an update for XtreemFS (version 1.2.1). This version contains mainly bug fixes, e.g. for FreeBSD and Fedora 12, and enhanced replica management. The new scrubber will automatically replace failed replicas.
Source code and packages are available for download on http://www.xtreemfs.org.
There is no change in the database or OSD storage, so an update from 1.2 should work out of the box. The usual advice: backup important data before upgrading.