I'd recently read this discussion on on the kerneltrap.org site about a
tool named 'fsx', originally developed by NeXT, which is used to test
and verify proper behavior in NFS and other filesystems.  Both FreeBSD
and Linux are mentioned as having problems.

  Major NFS Bugs Found & Being Fixed
  http://kerneltrap.org/article.php?sid=415

I looked through the recent archives of tech-kern but I didn't see any
reference to fsx there.  So, this would be worth investigating if it
hasn't been already.

-brian.