I remember seeing a French Mac many years ago (pre-OS X). I don't know what kind of mega it used (there was no giga back then), but file sizes were reported as "Mo" rather than "MB", for "mega-octets", "octet" being the French word for byte. It sounded much classier to me.

Of course, aficionados of RFCs will know that "octet" is (or at least was) the preferred term for "byte" in IETF documents as well. I don't think this is because the RFC editor was secretly French, although i'm sure he was thoroughly classy; presumably it's because early RFCs were written in the era when the byte had not quite settled down at eight bits, and needed to be unambiguous.

Snow Leopard apparently, which was released in 2009. Ubuntu's policies on the subject seem to be about the same age.

I suppose I should've said that up until five years ago, nearly everyone was using powers of two for file sizes. And Windows/Mac never used the correct prefixes.