I guess I'm asking more about the practical pain points. - As you say, I trust rails to deal with most of the day-to-day.
do you end up battling to get your postgres install working after upgrading mac (or postgres?)
You can install Postgres as a user-space application (with an icon and everything), so this can be a non-issue.
do you have problems with string encoding incompatibilities in obscure email addresses?
If it doesn't fit into UTF-8, then you may have a problem. Do you have a problem now, in MySQL? What encoding and charset are you using now?
do you have a convenient gui for browsing (like SequelPro)
TablePlus is pretty nice.
are there other similar annoyances, or does it 'just work'
Like another commenter posted, I have used it on Heroku with SQLite on the dev side, and no issues.
whatever I use, I like to stick with the same db in dev & production, ( using mysql or sqlite for my tests and postgres on the server seems like it is asking for trouble)
It could be a problem, or it could be a sign that you are depending on a database feature to hide a bug. At work, we use SQLite for testing (including the CI stuff on GitLab) and Oracle on the production server. We try for 100% test coverage.