Hi TK,
Sorry, I almost forgot about this thread. I kind of feel obligated to give some sort of answer here since you started the thread based on one of my comments from the Gay Christian thread.
Unfortunately, I don’t think I can give an answer that satisfies all the questions about this, but I’ll give it my best shot.
In my opinion, it’s a very complex issue because of the relational dynamics of marriage contrasted with the corporate and organizational dynamics of the modern church. Couple this with the fact that most people in our culture are so used to divorce as being normal, that there is a cognitive dissonance barrier to get over when someone is confronted with the idea that their divorce may actually be a sin in God’s eyes. Because of this, I think dealing with unjustifiable divorce may be a little trickier and take more time than your run of the mill obvious sin like fornication or blatant adultery.
My own opinion is that the issue needs to be dealt with more on a relational level rather than an organizational level (which is not to say the it shouldn't be the elders of the church). As Christians get to know each other, and discover certain things about each other (such as an unjustifiable divorce), my own thoughts are that it is to be approached delicately and prayerfully and with much counsel from others.
I’m kind of wimpy when it comes to the “thus saith the Bible” approach. It seems to me that more often than not, that approach ends up merely nuke-ing the relationship and destroying all avenues of helping bring someone to repentance. But I also think it’s too wimpy (and very irresponsible) to just ignore it altogether and pretend there is nothing to be addressed.
I’m most comfortable with asking pointed questions to people in hopes that the Holy Spirit works out the conviction in the heart of the person I’m confronting about some sin in their life. In our culture, I think a person owns the conviction more when it comes from within rather than imposed from another person. This is especially true if someone has no idea that they are in living in constant sin through and unjustified divorce and remarriage.
So I’m thinking of questions like:
What do you think it means to confess Jesus as Lord?
Is He still your Lord when He asks you to do something that doesn’t make sense to you or that you don’t agree with?
What do you think Jesus would say about divorce and remarriage in our day and age?
If Jesus were standing here right now and told you that your current marriage is adultery, what would you say to Him? What if He merely wrote it to you?
What do you think this verse means? (Matt 19:9)
Etc., Etc.
In my mind, it’s important to let people answer questions like these themselves and refrain (at first) from giving your own opinion on them. I think you'll know if they are being received or not. If they are truly seeking to submit to God, they will come up with the obvious answers. If not, then there are greater barriers to get over before they will believe that their divorce and remarriage is wrong.
I’m not sure the shunning thing would really work in our day and age. It’s too easy just to go to another church that doesn’t care about your sin.
Anyway, that’s the short of my opinion on this. For me, I have to take into consideration the culture and time we live in (that’s probably a weakness of mine

), and the level of commitment a Christian says they have. If they don't show signs of being totally committed to the Lordship of Christ, that's where they need to be before they will own a sin the rest of the culture winks at.
But that’s just where I’m at with this presently. Like I said, it's very complex IMO. And it’s one MAJOR reason I’m glad I’m not a church leader.
I suspect Steve would have a very different (and far better) point of view on this. Maybe he will chime in here.
Lord bless.