Here's a summary of my experience at the interview, which occured earlier this month.
Similar to the experience of others in this thread, my scheduled interview time was pushed back by 3 hours; I received notification of a revised appointment time the week before the interview. I wasn't sure whether this rescheduling meant anything (good or bad) in relation to the interview outcome, but it turned out to be be a complete non-factor.
I arrived 15 minutes before the revised scheduled time. I passed through security immediately (no line-up), was given a ticket number, powered down my phone and left it in one of the assigned lockers. Do not bring a large bag or laptop. I took the elevator to the first floor for processing.
There were about 15 people in the waiting room when I arrived. I think 4 of us were there for immigration interviews and others for various other reasons / visas. After 10 minutes my number was called to the first window/ kiosk for document verification. I provided the required documents (passport, birth and marriage certificate, passport sized photo, police checks, tax returns, etc.) and answered some questions:
Who is your petitioner?
What is your relationship with the petitioner?
When were you married?
What is your mailing address for the green card?
What is your partner's address?
Have you ever served in the military?
I was then asked to return to the waiting area and told they would call my number for the interview. While waiting it seemed that most interviews ahead of me took no more than 5-7 minutes. After a ~25 minute wait, they called my number to a different window for the interview. They had me confirm all information as accurate and truthful and then asked the following questions:
What is your name?
What is your partner's name?
What does your partner do for a living?
How did you meet?
When did you get married?
When and how long was the longest stay in the US*?
Which countries have you visited*?
In which countries have you lived?
Have you ever been arrested / commited a crime?
Have you ever served in the military?
Do you have any children together?
Have you or your partner ever been previously married?
Have you had a US visa before?
Have you ever been denied entry to a country?
*Due to my profession and frequent travel, I printed out an updated list of countries visited over the past 5 years and 5 most recent trips to the US and gave this to the officer. I'd recommend this as it seemed to be helpful for her.
The consular officer then told me she intended to approve my visa. The interview was probably 7-8 minutes in duration. After a 26 month wait (to the day) for approval, this was a welcome decision. I thanked her, collected my documents, went downstairs to retrieve my phone, and left. Two days later, having paid for expedited shipping, I received my passport with the immigrant visa stamp at my home address.
I came prepared with a large binder with all documents that I thought could be useful, including updated files from our original i130, DS260, and i864. I didn't need to retrieve any supplemental documents, but I would certainly recommend being over prepared. I had also scanned various websites for interview preparation to determine which questions might be asked. In my case I was asked the standard questions, but again, it's better to be over prepared.
Hope this helps others.