lianbear,
i'm in the same boat. this is what i know.
1) during your meeting with your WL manager, he/she will tell you something specific to do (ie, retake your gmat and get > 700, explain or rewrite an essay, etc.) OR simply tell you that they like you but want to compare you to the incoming candidates. (which i take to mean your app is good enough, but not enough that they aren't sure someone much better will come along. or maybe they have too many ppl from your demographic -ie asian/indian engineer or white investment banker- obviously they won't really explain the specifics). The WL Manager confirmed that they do have cases where they ask for specific improvement in one area of the app.
2) i would guess, esp since you have over a 700, your gmat is not a problem. I read one instance in the forum where someone on the CBS WL was told to retake the GMAT and shoot for > 700. So most likely you'll be told there's not much you can do except wait it out.
3) IF you feel like you can significantly improve your GMAT (750+) and take it soon, (before end of jan) i feel like you should try. I don't know how much it would help, but it absolutely would not hurt. (although, only if you have the time to study. i just retook mine, unfortunately i got the same score)
4) I wouldn't put too much stock in the interview. It's great that it went well and was 1.5 hrs, but since the interviewers can vary so much, it would be logical that CBS only really pays attention to it if the interview went horribly bad. mine went well, but was only 20 min, and she didn't ask any of the "CBS questions" that have been posted on this forum.
5) I know after all the work and the waiting, it can be quite disappointing to get the deferral letter, but to put things in perspective, CBS is a top 10 business school with a very low acceptance rate. ED is a bit easier, but it seems like at least half the applicants have been dinged outright, and i've seen some 3.8 770s among them. The fact that you've been deferred is NOT a rejection and there is still hope.
6) worst-case scenario, you'll get rejected, but it seems like there is a lot of favor towards reapps that were WL'ed the year before. there are def. different types of ding letters, and most WL'sters seem to get the one that encourages them to reapply next year. so if CBS is really the ONLY place you'll go to, i'd say your chances to get in either this year or next year are good.
my question to you is, why not accept the admission to INSEAD and just withdraw if you get into CBS? You'll lose your deposit, but at least you'll have the peace of mind that you're going to b-school. If you won't attend INSEAD, why'd you apply?
As i mentioned, you still have a shot at CBS this year (although i'll agree that i don't think our chances of getting in as deferrals this year is particularly high), and i think our chances next year are decent, but nothing is guaranteed. Whereas, you already have admission at a really good school already!
if you dont' mind, let us know what your WL manager tells you and good luck!