actually no I don't.
I could see where it would be amusing. I am friends with an ex on facebook but after how many years of not speaking we are on good terms and can be friends.
I guess it would depend on the relationship and if there has been enough time in the separation to gain closure and heal from the heartbreak.
If you haven't had that it could cause all kinds of drama and pain.
I've also had the relationship with an ex who has pretty much refused to give me the space I wanted from him to even be friends with him. There were too many emotions there and he never left me alone long enough to gain closure and perspective and has hurt me for years (yea I've written about him here on LJ lol). BUT I've never contacted him. He generally finds me and gets in touch with me.