Is it okay to have your ex as a friend on facebook?

Wassup blog readers? Bobjohnson is trying to settle an ongoing debate about ex-girlfriends/boyfriends. My question is: Is it okay to have an (ex)-that your (now) knows about, as a friend on Facebook.
I have asked this question before and I have received mixed responses. Some say that it is not okay because once a relationship is over all ties should be cut. But others believe that just because you are not in a relationship does not mean that you can't be friends. Yet others say that it depends on the circumstances.
What do you think?

http://www.youtube.com/watch?v=84BGaBCVWhM