I only have one actual proper ex to speak of, and although she is well aware (I hope) that the door is always open, I seriously doubt that she'll ever make any attempt to contact me.
Although I have occasionally looked up her name on Friends Reunited and Facebook, but to no avail.
Other exes - people I've been out with for a few weeks max - most I'm not in any real contact with anyway. One I am still on good terms with, and she came to mine & Sarah's wedding, but AFAIK she's not on Livejournal or any other social networking site. If she were to Friend me on any such site, I'd certainly reciprocate. In fact I'm thinking I'd like to get in touch with her and maybe touch base with her sometime over the Christmas holidays.