I will admit I'm more like to use "--" and not bother converting it if not done automatically on quick forum posts. You can find examples in my post history. But I come across them all the time in written works.

Because parentheticals—as aside, explanation, enumeration—aren't taught and we are left to learn them by example, and not many people care enough about writing style to pick up on them and want to use them. Ask most people who don't deal with technical writing about the Oxford comma and they likely won't care, if they know what it is in the first place.