It's pretty common in the UK these days.
In situations where it doesn't matter (and that's most of them) I've stopped correcting people who assume we're married and I've taken my partner's surname.
It actually makes things easier. If they assume you're married, they generally have no problem talking to you about whatever they called to talk to your partner about. When they find out you're not married, sometimes suddenly you can't be trusted.
If they want to assume I'm Mrs so-so, rather than Ms so, partner of Mr so-so, and that gets me better service, then I don't correct them.
If they ask directly, for whatever reason, I don't lie.