As an FB employee, I use hg regularly (because it is required). I would not use it as a git replacement for non-FB-sized repos. It has some weird design choices (e.g. branching is bad), and it very often requires manual intervention for merges that git performs correctly and automatically.
You can get around branching-is-bad by changing your workflows a bit, but you can't get around the bad merges: over time it's like death by a thousand papercuts.
You can get around branching-is-bad by changing your workflows a bit, but you can't get around the bad merges: over time it's like death by a thousand papercuts.