There has been a back and forth on formal ChangeLogs vs vcs commit messages via the GNOME mailing lists. Doing the latter exclusively has never sat well with me because I think it weakens good development practices (at least mine). I find many vcs commit messages lack the detail of ChangeLog commits generated by a workflow involving C-x-4-a in emacs for instance, which makes in easier to document changes on a per function basis, and that makes it easier for others to understand the changes that were made. And documenting on a per function basis forces me to review my patch prior to commit (good practice anyhow, but this puts it in my workflow).