Scenario: After your last commit, you decided to do some extensive refactoring of the codebase. After a time, you realize it is taking longer than expected, and you'd really rather put off the refactoring for another time, and work on more pressing tasks. But you don't want to lose all of the refactoring work you've done so far.
So, is there a way to "archive" or "branch" the working copy (essentially, set it aside but keep it in the repository for later access), and then revert to the last good commit and resume from there, without fear of creating multiple heads or getting the two mixed up?
Don't worry about "the fear of two heads". Two heads is a very normal state. It's called anonymous branches, and it's one of the ways people do temporary branches in Mercurial.
Just commit, and then update to tip-1 and you're ready to go:
hg commit -m "working on XXX"
hg update -r "tip-1"
and away you go. If you want to drop a bookmark (less permanent than a tag) on that head you can, but there's no need to worry about it.
You can always push one head without pushing another using hg push -r HEAD where that can even be hg push -r .
Don't fear heads -- they're what makes a DAG based VCS powerful.