one day "supersed" became a dep on something installed, so it got emerge -u worlded. later i needed to compile mozilla. supersed (being invoked as "sed" within the ebuild) blows up with "internal sed error" and mozilla fails to even reach the src_compile stage. supersed probably needs to be installed as "ssed" rather than "sed" (currently supersed clobbers sed). i'm not near my dev box atm to fix this, so i'll just leave this note.
matt, if you can duplicate this, can you possibly e-mail the supersed maintainer with the info? thing is, supersed will become GNU/sed-4.x in due course, so this would help him fix things upstream
supersed now installs as /bin/ssed instead of /bin/sed, so this problem should go away, but I would still like to have this bug reported to the supersed author.