Well, I can report a positive experience just over a year ago. In and out of the Belfast Embassy for the interview within 2 hours. Arrived in Orlando and sent off to the immigration room, 20 mins later and a quick chat (they'd never heard of Kazakhstan where I'd been 2 months prior on business and thought I may be a communist - but easily resolved) and I was through immigration and done. Piece of cake.
However, I would say - get your bottles in a row before you go to the interview. Make sure you have the proper U.S. passport photos (not UK size) and that you have everything they want - and that you've paid for the interview and have a receipt!
If you have it all boxed off, it's a no brainer. I counted 5 people before me in the queue who got bumped out of the embassy as they didn't have the required docs - and that's after the 2 hour wait!
But it worked like a charm for me!
