Pros
SpaceX is changing the world - the company's goal is literally to colonize Mars, and revolutionize the entire space industry in the process. Every day this awesome sense of purpose is sitting there in the back of your mind. We work with the best and brightest engineers in the world, but our scrappy, hands-on, experimental attitude prevents any kind of ivory tower complex. It's all about daring greatly.
Cons
The work here is difficult, and you're expected to get it done fast. The reports of universal 80 hour weeks are simply not true, however. I've been here for 5 years and have certainly done my stints of late night and weekend work, but as the company has grown the manic drive has ebbed (in no small part because the core of the company is no longer in their 20s). that's either a pro or con depending on your stance, but the point is you can make your own way here. Deadlines and priorities are fast moving targets. You will have to learn to let go of frustration when your year long project gets canned or the deadline you've killed yourself for a month to hit gets pushed out by six weeks at the last minute.