Pros
The excitement of making a difference in a company that has such an ambitious goal is the best part. The culture is great. Everybody is focused on getting work done and try to avoid bulls**t politics and wasteful meetings whenever possible. People support each other as a team rather than trying to get ahead of one another. Interns are given projects that will have a large impact across the company instead of having an insignificant role like interns at other companies. Good hourly rate for interns and plenty of overtime available. Cheap, good food is available for all meals at work. Seeing all the cool stuff SpaceX only shares internally.
Cons
Long work weeks (around 50 hr/week) are considered standard though you may be able to work less depending on department. The location in Hawthorne is not amazing so you can either live in that poor location or take about a half hour commute in from somewhere nice (like Marina Del Ray where they house interns). You can't take pictures or share any of the awesome things you see/do with your buddies.