I've always made a habit of putting /usr on a separate partition to /. No particular reason, other than the usual arguments for a small root partition. Imagine my surprise when my alpha failed to boot one fine day a while ago.
The problem was that libgpm moved from /lib to /usr/lib. And bash required it. I can't find anything in policy to say that all library dependencies for binaries in /bin should be in /lib; should there be such a rule? Or shall we not support a separate /usr partition? m.