[przemoc]

It always felt natural to put this dot at the end of (what antirez nicely called) commit synopsis, so AFAIR I always (or at least since I started using git and when was not forced by particular project's rules to do some other way) put it there and found advices to avoid it quite strange. The only exception (beside forgetting about full stop yet pushing to public repo, it does happen sometimes) I have is when the commit is sole version-bumping/releasing one, because then I usually go with following style

    PROJECT_NAME [v]VERSION

There are some half-broken SCM managers that always display whole commit message (sometimes even without respecting paragraphs) and then such synopsis without full stop yet followed by another sentences looks rather awful. YMMV

As some commenters here already wrote, it's not a grave matter, but it's good to have consistent style. It goes without saying, that having relatively short commit summary in one sentence separated with blank line from further details (if they are necessary) is far more important matter than the period or lack thereof, as it immensely eases groking commit log.