We've hit this issue recently when building software packages for multiple architectures.
I believe the general consensus is we should order things, but another point to discuss is the specific ordering Debian should use.
IOhannes' example lists libc.conf earlier in the ordering, putting /usr/local/lib before /usr/lib/$(uname -m)-linux-gnu.
My colleagues and I agree that this is preferred for us, since this enables the local administrator to effectively overwrite system-defined libraries, if they so choose.
Thoughts?