At work we use XFS primarily on / to allow us greater flexibility with file size, filesystem size, and inode limits. It's been working out great until FC6 came out. For some reason when you install an FC6 system using xfs (boot the install with "linux xfs"), the install goes great, but the system can't seem to write to the drive after it reboots. I'm not sure what the bug is all about, but it's been reported and is being discussed on Redhat's Bugzilla (XFS on FC6)
I think I've found a workaround that seems to do the job. If you install the system with selinux disabled (linux selinux=0 xfs), the system will boot up just fine. If you really want re-enable selinux, you can re-enable it after first boot (edit /etc/selinux/config) and reboot to apply the change.