It's used quite commonly by native English speakers in Canada.

I've only ever heard it in movies, but I think all native speakers will understand what it means.

Yes, it is used in the UK, though mainly by older people.

Some people use it here in the States. It's not extremely common, though.

Yes, it's used enough to be recognised. Sometimes, English speakers use a French phrase for certain situations. I'd expect to hear it more often in the UK, as they are France's neighbour and all.