What would an OS says or think when copying files - let's say, about 100MB of MP3 - to an SD card?

DOS

What's an SD card?

Linux (bash)

....
....
Done.

Windows XP

Alright. Wait around a bit, and it'll be done. Don't ask me when, because I'm terrible at guessing.

Windows Vista

What? Me? Do you have any idea what you're asking of me? It requires careful planning: first see whether it all fits on your card, then calculating the time, and even then, I'm not sure if I'll do it. Maybe you should check back tomorrow; maybe I've gotten around to it by then, just maybe...