I am not sure if the other reviews are particularly biased or there's a tendency to depict more negative things than positive ones, but I have to admit that my experience differed significantly from the majority expressed here, namely no ghosting, super polite and professional people, complete availability.
The process has been a very comprehensive one:
1. First Recruiter screen: the HR representative goes through your person (and your CV) to understand if you can be a good fit. Here they tend to analyze both your skills as a whole (high level) but specifically the person - they do care a lot about how well you can get along with your peers
2. First phone interview: one of the people you may be working with does a general quasi-technical interview. He/She tries to get a grasp on your reasoning skills and how well you could do in the following steps of the interview process. If the conversation goes forward smoothly there are no reasons to deny the other interview steps. This is more a pass/no pass section, in my opinion
3. Take home assignment: depending on your department/group and your tasks, a specific TOA is given in which you have to understand a broad problem and provide your analytical insight/solving skills in coding. There are no "super right" answers, they try to understand how you face and how you reason in front of a problem similar to the ones you may face if you're hired. If you are kinda new to the programming language they request/assign, do your best honestly: it may show your learning curve!
4. "On-Site" Interviews; here you have a series of 30-45-60 (depending on the type/number of people involved) minutes interviews with different people you may be working with. Some may ask to describe your reasoning behind the TOA, others some sort of live whiteboarding on easier tasks compared to the TOA (but you code there on the spot), and then technical interviews more on your role.
From the start to the offer the process took 8 weeks; a few days for the first screen call, then all the other processes on a week/bi-week separation.
People at Planet are truly people of the Planet Earth. They DO care about people and care about you. They're generally young, energetic professionals that do believe in the company's goal. The group of people I interviewed with has been superb and I enjoyed every bit of the process, even though it was my first non-grant set of interviews.
HR people nicely guided me during the whole process. I have been put in contact with four different HR people due to appointments/events (vacation at one point, then another one changed the job) - nevertheless, the process was super smooth and I did not feel like they were shifting me from a person to another, but as if a different HR person was positively guiding me to the next step.