One of the supervisors called me quite late in the evening to schedule for an interview the following week that had the interview listed as from 1pm to 7pm, but be there by 11:30am. Details of interview were not really given other then when to show up. Showed up on time and found that 4 people were also scheduled the same time as me. We were escorted in to a small hallway to wait to be interviewed. My interview was not to start until 2pm, but I was already waiting at 12 so I just reviewed notes. It was a bit uncomfortable considering workers were walking in and out and the long waiting period was not helping with being nervous. Got into the interview interviewed by two supervisors. The lady asked a few questions but mainly let the man run the interview. He asked me about why I wanted to work at Genentech and some technical questions about running machines. I only got about 5 basic questions when he said he was tired and wanted to end the interview earlier. I already felt awkward with the interview style, so I of course did not expect any offer, but it was an experience.

Informal, though they may do it differently each time. I had a 3-panel interview and was immediately notified within a couple of days that they wanted to move forward. As long as you are open to learning and can get along with the interviewers, you should be ok.