However, I have yet to see an mv command that would transparently handle the moving of a directory from one filesystem to another. Are you aware of even one?

• Mandrake Linux 8.2
  Edited output from mount:
  /dev/scsi/host0/bus0/target0/lun0/part9 on /tmp type reiserfs (rw)
  /dev/scsi/host0/bus0/target1/lun0/part2 on /home type reiserfs (rw)
  # mkdir /home/test
  # touch /home/test/testing
  # ls -la /tmp/test
  ls: /tmp/test: No such file or directory
  # mv /home/test /tmp
  # ls -la /tmp/test
  total 8
  drwxr-xr-x 2 root root 72 Jun 28 09:26 ./
  drwxrwxrwt 106 root root 6736 Jun 28 09:26 ../
  -rw-r--r-- 1 root root 0 Jun 28 09:26 testing
  
• HP-UX 11.00
  Edited output from mount:
  /tmp on /dev/vg00/lvol4 delaylog,nodatainlog on Fri May 10 15:37:38 2002
  /home on /dev/vg00/lvol5 delaylog,nodatainlog on Fri May 10 15:37:38 2002
  # mkdir /home/test
  # touch /home/test/testing
  # ls -la /tmp/test
  /tmp/test not found
  # mv /home/test /tmp
  # ls -la /tmp/test
  total 10
  drwxr-xr-x 2 root sys 96 Jun 28 09:40 .
  drwxrwxrwx 9 bin bin 5120 Jun 28 09:41 ..
  -rw-r--r-- 1 root sys 0 Jun 28 09:40 testing