Honest question - how important is a CS degree in silicon valley? I ask because I'm halfway through majors in systems engineering and physics, and I'm now realizing how important CS is and how much I enjoy it, but I figure that my quantitative background with the ability to program is equally marketable as a CS degree.
It depends what you're doing and where you want to work, but it's competitive: you're going to need a technical degree with a very good grade average to get in the front door at a lot of companies. Systems engineering and physics will probably stand you in very good stead.
I'm not in silicon valley, but just a question for your question: If you want to do any kind of hot-shot software development as a career, why would you study systems engineering and physics? It seems like an oblique way to go, kind of like getting a statistics degree if you want to do pure math research. Within a CS degree there is also a lot of room for your own interests, many of which are highly quantitative.
It's important if you want to get a job. Not so much if you want to start your own business (see my other comment in this thread for more details on that.)