Shortly before my first interview, I had talked to the Nerd Hunter at an Open House at the Nerdery, so he gave me the option of skipping my first interview and going straight to the Code Challenge. I did the challenge and sent it back in within a week, and another week after that got an invitation to a second interview. In the second interview, I was given feedback on my Code Challenge by one of the senior developers, and then one of the Associate Directors of Development asked me more about my résumé and skills. We then had a chance to talk more generally about the position and the company, and I had plenty of opportunity to ask questions. I was asked what kind of salary I was looking for. I got the job offer via email the next afternoon, and the salary I was offered was $5,000 less than I told them I'd been making at my previous job.
During my second interview I did get a tour of the place, but the Open House gave me the most insight into the company and the work culture. I asked everyone I met at the Open House if they could tell me even one bad thing about working there, and I got answers like "My commute got longer" or "I wish the free food was healthier." The employees at the Open House were also giving me advice for the interview process, including to not dress too formally for the interviews and to try to turn in the Code Challenge a few days before the official deadline (I was given a week, and turned it in after four days).
I wasn't asked many stereotypical interview questions, like "What's your biggest weakness" or "Describe a difficult situation you dealt with at work." It was all casual, upfront conversation about my skills and my reasons for wanting to work there. On the application, when asked what made me stand out amongst other applicants, I mentioned that I had a strong desire for learning new things all the time. I was told in my 2nd interview that most of the other employees there gave similar answers to that question.
The best advice I got was to be completely authentic in all stages of the hiring process: on my résumé, on my application, and in my interviews. Have a good sense of humor about yourself, and don't hide any quirky things about yourself—showing them off will probably earn you bonus points. I had an entire "Nerd Cred" section on my résumé that went over pretty well, and it included things like being a kickass healer in World of Warcraft and having several publicly released WordPress plugins.
Also, don't be intimidated if you don't have a 4-year degree. A lot of the employees there have 2-year college degrees or none at all. Equivalent work experience is considered just as valuable (I had 6 years of experience and a 2-year degree).