create one program that does massive sequential writes to a file in one directory.
then do a fsync on some file in a different directory (with a small change to the file)
watch the fsync take a long time to complete on ext3, and almost no time on any other filesystem.
because of this behavior, users and sloppy programmers have been conditioned that fsync calls make their program pause unexpectedly for a potentially long time period (I think I've seen Ted Tso report that he's seen delays longer than 30 seconds)
If you go back the the blog messages about fsync and data reliability when people were claiming that ext4 was eating their KDE configuration data, you will see detailed discussions about this.