Applied online on MIT webiste. First talked to a general HR recruiter. Then set up a skype interview with the professor. The interview was a bit bumpy, but I guess this person must have liked me very much because I ended up his first choice. Just asked standard questions about research experience and career goals, management style, etc. Then I got another pushy phone call from the HR person asking me to decide within a day whether to accept or not. I did not like dealing with the HR department but I absolutely love my professor very much.

She was friendly but they didn't specify what was needed for the position so I was rejected. But they were both very nice and very fast with the process. Overall an okay interview.