I tested the exact same thing again but waited 60 seconds after saving
the file, and then yanked the power out. Upon a boot up, the file was
intact and the save worked. So you still have about a 60 second window
of newly written files and a power loss for data corruption, unless
the program can sync it to disk before that.
Well I'm only passing on what the XFS devs have said, all of my boxes are
on UPSes so I rarely saw the issue anyway. But are you sure the squares you
saw in the word doc were nulls? The FAQ page says that you can use the
xfs_bmap command to see if it has any extents allocated and if it does then
it would likely be another issue.