How about we think of facebook in terms of actual sociological tendencies instead of cynical lowbrow humor. Facebook is a result, not a catalyst. Facebook is a result of communities as well as the entire globe, evolving their relationships towards a different orientation: one that involves other people. Being permanently connected with old flames isn't going to affect the divorce rate, or any other significant stat.... those stats are affected by changes in culture in a much bigger picture.
I have 2 ex-gf's on facebook... I've spoken with one of them twice in the last 2 years... and neither exchange was flirtatious. If I found them desireable, I'd still be with them.