My wife and I just finished the GC interview at SFO office. Here is some experience to share. I've been tracking this forum for long time and my impression was the interview was nothing but a little chitchat. It turned out our interview was much tougher. After about 20 minutes after we turned in our interview notice letter, we were summoned in followed by some standard procedure e.g. taking finger print, taking the oath... Then the officer started querying us. He first asked us about some very general questions such as name, address, spouse's birtherday, how many times we have entered the US, in what status. Nothing tricky there. The the officer started looking into my company's 2001 federal income tax return which signaled me some trouble. Because we are a small company and most of the employees are foreigners. Then the officer told us that the reason our case was transferred to local was that the company's revenue was pretty high while the payroll part was relatively low. And also, most of the employees are applying for GC so the CSC suspected that the company was helping us get GC by underpaying us. My attorney explained that when my labor was filed 3 years ago, it was really hard to find qualified american people and my salary was based on the prevailing wage. Then the officer asked me how many employees we still have now, has the company laid off any employee recently. I was really scared at that point. Then the officer noticed that I used my EAD worked for another company for 2 months earlier this year, he asked me if my employer was OK about my leave at that point. He finally close all the folders and took out a piece of paper from the drawer. I almost sh*ted on my pants 'cause I thought he was asking for some more documents. I just couldn't afford another round of inquiry. Then the officer told us that the files looked good and were ready to approve. Since they newly added a procedure that every GC approval must wait for FBI clearance, he couldn't stamp my passport right now. The paper states wait for security clearance and he told us it could take up to 4 months. While my lawyer told me afterwards that it may just take a month based on her experience. That was the end of our 45-minute ordeal.
My thinking is, everyone requires interview must have something wrong/fishy in their case. So before you walk in, review everything and have your story ready if necessary. Good luck everyone.