I am a current student at Yale, and I had been on the wait list. I was offered admission on 23 January. My results may be slightly a typical as I am currently on active duty in the Army and I had to know by 31 January or the Army would not send me to Yale period. I made that clear when I sent them my update, and that they were my first choice.
I was so surprised that I was getting off the wait list in January and I asked the ADCOM what caused the change. She said they do a review of the wait list after the deadline for round 2 submissions.
The advice in the articles posted by Jontron is essentially what I did. Actually, I did almost every single bullet point. I gave one very thorough and polished update at the beginning of January. The really great thing about this update opportunity is that you are not constrained by formatting. You can make it look really really good. I also found ways to address every single potential weakness. My final packet was 10 pages and included:
1. Promotion
2. Complete rewrite of MBA purpose essay and made it slightly more ambitious, but not fictional.
3. I actually clarified some interview questions i felt i did not answer well (no one recommends this but I thought it could really help my situation)
4. Past performance reviews from my military schools outside of undergrad to compensate for GPA
5. Letter Stating that Yale was my #1 choice and I would accept immediately, but that I needed to know by 31 January.
I put into a PDF portfolio with links and tried to make it look professional, I am sure others could do better with tools available out there.
I scoured the web for info last year, so here is a success story. I do not know what parts if any of my update helped, but I did make it in. Good luck to everyone. Feel free to PM me if you have any other questions.