* Git octopus merges
* Mercurial descriptions that are not UTF-8
* Git commits whose messages aren't in their nominal encoding
* Mercurial and Git having invalid timestamps
* Git having a different author from committer
* Git and Mercurial commits and changesets with extra metadata
* Mercurial usernames that are not valid Git usernames
* Mercurial bookmarks that are not valid Git refs
* Mercurial named branches
* Git annotated tags (requires an not-quite-yet-released extension to fully round-trip; the non-annotated part of the tag works today and will be forwards-compatible)
* Mercurial changesets/manifests/filelogs with bad parent data
* Git trees that are just flat-up invalid
* Subrepos and submodules (100% preservation, but we can only
translate Git submodules/subrepos cleanly to/from each other,
since Git submodules have to be Git)
Anyone intelligent enough to use git or hg should be pragmatic enough to learn the other one for the benefit of the smooth workflow, when presented with this list ?
"Git master branch in sync with the Mercurial repository’s tip transparently. So far, so good."
Did you mean "default" instead of "tip"?
(This is hard to handle for normal git users as well, but it can be nice in some edge cases)