I think working on software at SpaceX would be seriously cool, but for unrelated reasons now's not a good time for me to pursue such a dream. I do want to make a move to something like spaceflight eventually - sort of a childhood dream of mine. If I may ask, are there any open-source projects or other technologies you would recommend for someone to work on if they wanted to prepare for such a career a few years from now? Currently I work primarily with with distributed systems / Linux distributions if that affects your suggestions at all... I've heard from some other friends that Ada is a must-have and that Matlab's Simulink is the future - but they do government work exclusively, so I'm not sure how it compares to a "space startup" like you.
I don't think you need to learn Ada! Take a look at our Reddit AMA for some details about what we use - http://www.reddit.com/comments/1853ap. There are a lot of different paths people have taken to get to the software team here, so a strong background with open source on some meaty distributed systems projects in Linux sounds like a good starting point.
