Facebook is also frequently cited in divorces because it's easy to gather "evidence" about their spouse's inappropriate actions through Facebook and use it against them in Court. Anything and everything you post on-line can and will be used against you. Be careful!
My advice regarding Facebook would be:-Avoid Facebook when you're mad at your spouse. There is just too much temptation.
-If you are trying to mend a struggling marriage, don't "friend" or "poke" old flings.-Don't share intimate details about your life/thoughts with "friends" of the opposite sex. Keep it surface level information.
-Keep your profile private and only accept friends (that are not a temptation) and relatives (If you like them...)-Keep an open policy with your spouse regarding user id's/passwords. It shouldn't be a problem,
if you have nothing to hide.
-As with anything, use it responsibly