This article is timely for me as I just brought up a new Scientific Linux 6.2 (RHEL clone) server last week that uses XFS for most of the storage. This is my first new attempt to use XFS in years.
At one point, I tried very much to make a go with XFS but I always ran into compatibility issues that made me regret it. Thankfully, I never had any of the reliability problems that XFS used to suffer from when running on commodity (unreliable) hardware. It feels though that XFS on Linux has finally grown up.
SGI Altix customers, like NASA, run XFS systems in the hundreds of terabytes (although I am sure some of those are CXFS). Also, XFS is a fully supported filesystem in RHEL6 (including xfsprogs). My understanding is that Red Hat now employs the majority of the XFS developers.
Filesystem of the future? Btrfs and ZFS are more feature rich although adding LVM2 and mdraid to XFS closes the gap. Of course, even that setup lacks deduplication. That said, given the performance and current stability of XFS, perhaps it is the right filesystem for today.