Git notes were used at the LibreOffice project to track, for each commit to the Apache OpenOffice repository (which they mirrored as a branch on LibreOffice's git repository), whether that commit was not relevant (for instance, changes to the build system which LibreOffice had long replaced with a better one), duplicated an already existing change on LibreOffice (often from many years earlier), or, the least common case, that it was accepted into LibreOffice (and which commit did the cherry-pick). You can still see it for itself at https://cgit.freedesktop.org/libreoffice/core/log/?h=aoo/tru... (that git front-end still displays notes).

(They stopped tracking these changes a few years ago, probably because the pace of changes to Apache OpenOffice slowed down to a trickle, and there's no longer much to be gained by cherry-picking these few changes.)