I personally don't keep up with my exes via Facebook, phone calls, or texting, but I have many friends (usually the currently single ones) who have added each other as friends on Facebook and MySpace and keep in contact that way.
Whether they're playing with fire, completely and utterly mature, or just think that electronic relationships aren't the same as regular friendships, I think it says a lot about you.
How do you feel about exes and Facebook, MySpace, texting, or any other kind of tech communication? Kosher or not kosher? Facebook friends until one of you is coupled?