I'd say it depends on what both feel. If one of the couple is still in love with the other after breaking up, it will NEVER work out, as the person in love will probably try to get the other one back. At least that's why it wouldn't work out for me to just be friends with my current boyfriend if he ever broke up with me. I love this guy, I can't just be friends with him.

That's why I couldn't stand staying friends with my ex right after breaking up. I needed about one year to be sure that I'm not in love with him anymore. Since then we've been friends.... on an irregular basis, that is, because he started moving from one city to the other after we broke up, but... we TRY to stay in contact.