I don't know about Mark's install, but the only things that go into the RAM fs are temporary files which can just be binned anyway. When I need to make changes to system-level stuff (new packages, kernel rebuild and the like) I just type rw and the filesystem remounts read/write (in true empeg style). Once I'm done, I issue a ro which puts the card back into read only mode. My home folder is mounted over NFS.