Here's a little tip for you.

If you run Ubuntu and decide to make a quick backup of your home directory using cp -R -d, make sure to "eject" any network shares you mounted using the file browser.

I just found out that despite the -d (which doesn't go inside symbolic links but has no affect on nautilus mounted shares) it was trying to back up a mounted network share... that contained about 15 cd-rom images of various versions of Ubuntu. That might take a while.