"Whom do you see?"
Translation:Wen siehst du?
I swear I've seen "wem siehst du?" somewhere around here. Now suddenly it's "wen".
I think you might have seen 'wem schreibst du?' i.e. 'whom are you writing TO' (or 'TO whom are you writing?). I think that's the difference.
I don't agree that it is "great English". Although they are often used interchangeably, that doesn't mean that it's correct; there is a distinction to be made in the usage of who and whom. Who is a subject pronoun and whom is an object pronoun. They are not the same thing.