Had my interview yesterday, so thought I would document my experience in case of interest to anyone going through same thing.
Interview letter stated time of interview 9am for myself and my 3 children. I arrived at the Embassy at 7.30am and there were about 100 people already queuing outside. Some of the people in the line said that there was one line for 8am interviews, 8.30 and 9am, but this was not true, there was one line to check in your name and be ticked off a list, one line once this had been done and then one line to enter the embassy.
Each person was allowed a small bag and mobile phones and any other metal items were put into a plastic bag which the embassy provided before going through airport type security. Laptops could not be taken into the Embassy and had to be left at the nearby chemist for a charge, and people could not go into the Embassy if they had not previously let the Embassy know, as some people were trying to do. Bags were checked, but just a quick look inside. It took about 45 mins before I went into Embassy and was sitting down by 8.15am
Once inside the Embassy, you went to a reception desk to let them know you had arrived and showed them your passport and interview letter and were given a sticker with a number on it either Ixxx or Nxx or Vxx e.g I366. This was your number to be called to a window.
There was a huge waiting room in the Embassy filled with chairs and a big screen that was showing which numbers were called to which window. Numbers were random and it didn't seem to matter which interview time you had been given, more when you had arrived. Numbers went onto the screen every few second, so this kept us all more than busy watching for our number in case we missed it! There were public toilets at the Embassy and also a small stall selling tea, coffee, water and small selection of snacks while you were waiting.
Along one wall there are a row of windows with people behind glass, and when your number is called you go up to the window to give them their documents. We were called around 9am.
Although they were behind glass the lady we spoke to was very friendly and courteous and lovely with the children. There was no rush and she asked for each document by name e.g. passport, birth certificate and copy, police certificate etc. and chatted as we handed each one over and she put these into a folder. She asked me if I had been to the States before, if my children were adopted and I had gone by any other name apart from my maiden name. She checked my contact details which had changed since submission of documents and she changed my address manually on the computer. She gave me an envelope with a CD of my chest x ray from the medical and said I had to give that to Immigration when I arrived in the States.
We then had to go to another window to pay our visa fee, which I did with a debit card. I was given a receipt which I took back to the lady at the window which she put into my folder. When she had all the documents she asked us to return to our seats and wait for our number to be called for our interview. We were called around 10am and had to go to another window to speak to another very pleasant man behind glass. He went through my folder and asked me how I met my husband, how long we had been together and what his job was. I had a swear an oath that what I said in the documents was the truth and had to put my fingerprints on the scanner for myself and for each of the children. All the time he was chatting more than asking questions and then said that the application had been approved and I would receive passports back in two weeks time. He wished me and the children the best of luck in our new life.
We were then free to leave the Embassy by which time was about 10.20am.
Very pleased. Now back to pack final things and wait for passports to arrive.
Forgot to add - huge thank you for all of the advice on the forum - made such a difference

Congrats

You won't need the CD at the border by the way, they always say that and it never gets taken.

Congratulations - exciting!

I heard mobile phones were now allowed in the embassy but was still nervous to try it but i guess now its OK!
Glad it all went Ok!