Really straightforward - I had one extremely brief phone interview (~10mins) with a recruiter to (I assume) judge the seriousness of my qualifications. He then scheduled a phone interview with a hiring manager for later that week.
Hiring manager phone interview was quite a bit more in depth, went in to my background and technical areas of expertise, was about 30 mins. Asked lots of questions about my work process and philosophy.
Heard back from a scheduler a few days later to set up an in-person interview. Four hours long, one hour blocks with two people in each. They also had me fill out a paper application with the usual info, nothing unexpected.
First round of interviews was okay, however one of the interviewers was 50 minutes late and that made the end extremely rushed. Other interviewer wasn't comfortable really digging in without the other present, so it ended up being an hour long general chat. He asked me mostly culture fit questions when he asked anything, talked a lot about work history.
Second round of interview was pretty tough. Two very high level programmers grilled me on my technical skills, looking to see where my limit was. They easily found it, but then circled back to try to re-ask questions from before in other ways. I ended up knowing more than I realized once they explained their questions a little more. Extremely friendly, and even gave me some super short and sweet Python lessons on finer points I wasn't familiar with.
Third round was general technical screening questions. Asked general stuff about server software, DNS, HTTP, etc. Asked lots of questions about testing and QA. Some more general interview questions and whiteboarding as well.
Final round was with the hiring manager and one of the lead programmers from the team. Extremely friendly, wanted to talk mostly about team and culture fit. Asked lots of general interview questions like "Describe a time when you resolved a disagreement with a team member."
Still waiting to hear back from HR, was told I should have a decision either way within a week.