I took a risk earlier this year and went with XFS for the filesystem on everbody.org. I chose it because it was very mature, portable, and supported quotas in the metadata. Other filesystems use special files to support journaling or quotas, but this seemed too fragile to me.
There was a risk, though, since XFS hadn’t been merged with the main kernel tree. The risk was that it would later be unsupported. The latest summary of changes for 2.5 indicates that XFS has been merged with the main tree! I was afraid it wouldn’t make it.