The first interview was a phone screen with the technical recruiter. It was mostly an opportunity to hear about the state of LinkedIn and see if it's a good fit for you. The recruiter asked me about my current skills and roles.
The second phone call was with a two session, 45 minutes each, phone code challenge using collabedit. The questions were both frontend questions about markup, css and javascript. If you know these three intimately, you'll be okay.
The developers I talked with were really great and were really interested in talking through the process with you, so don't get carried away just typing, talk through your process.
The last interview was an onsite.
The recruiter met me at the lobby and walked with me to the interview room and explained to me how the interview process was going to go. They give you an itinerary with everyone's name on it, which is really nice to offload one more thing you have to stress about through the day. We had a great conversation about what the recruiter liked about LinkedIn, about where I currently work and just life in general until my first technical interview.
Each technical interview (of which there were 7 questions), was about an hour, and a mix of culture/skills questions and whiteboard questions. These questions ranged from moderate to difficult, and they all require you to think through the process of solving the problem.
You really need to know html and css with 100% certainty, and you need to know your javascript well. There were two CSS challenges and 5 javascript challenges, almost all of them involved also writing the markup to correlate with them.
Overall, this has been the best interview experience I've ever had, and I've had some really great interview experiences. LinkedIn seems like the kind of place anyone with a passion for development/engineering would love to be.