Pros
This is an incredibly exciting and inspiring place to work. Even when you're tired and have a lot to do, it is amazing to be able to work on furthering humanity's reach into space. SpaceX is constantly innovating, and the employees are all so passionate about their work that they foster a very energetic atmosphere. I have also found that SpaceX is an excellent place for those who enjoy a challenge. You are expected to hit the ground running upon starting, and learn to do your job by doing your job - there are no extended orientation/training periods here. Luckily, anyone I have ever asked for help or clarification as to what I should do has been very helpful. The relatively horizontal hierarchy at SpaceX and culture of constant learning means that it is very easy to ask questions of anyone if you need help.
Cons
One of the big "cons" that people talk about is difficulty with work-life balance. It can be a problem, especially if you have a big deadline coming up. Some people seem to be here 24/7. But the focus is on getting things done rather than spending a lot of time at work. I get everything I need to do done without needing to be at my desk 16 hours a day, and leave when I feel like it. It is easy to feel like you must appear to be working all the time, but it is up to you not to get sucked into that. Perhaps I might feel differently after a longer period working here, but at the moment I am maintaining a routine that I know I will be able to sustain long-term and which gives me enough time away from work to keep me excited about what I do. I also feel that sometimes there is inconsistency across different groups in the company as to how they document work. This is sometimes frustrating to me as I need to work with a number of different people and cannot always find their documentation. However, that is a fairly minor annoyance and the introduction of some new systems is starting to help.