Junio C Hamano, Sun 2011-11-20 @ 13:16:27-0800:
> We do not have "not tracked, but precious (e.g. your TODO)" category;
> from time to time we have discussed possibilities of adding such to
> enrich the categorization, but nobody stepped up to actually do the
> work of designing let alone coding such a beast.

If I'm not mistaken, files ignored by .git/info/exclude rather than
.gitignore do exhibit this behavior. That is, Git will refuse a checkout
with an error message if it would overwrite a path listed in that file.

I don't know if that's actually intended behavior, but I've noticed it
before and made use of it.