I'm currently finishing my PhD in Biology here at UCSD. This was a big change from physics and I am not directly doing much physics related research. However, I think my physics training was very important. I learned how to be a clear, critical, scientific thinker which has served me well here. Having a physics background in no way hindered my applications to biology graduate schools. I think most schools considered it an advantage. The field of biology is becoming much more analytical and the perspective I have with a physics background is quite useful. Now that I am looking for a job, I think having a background in both physics and biology will help a lot.

I use my physics knowledge to allow me to quickly grasp the underlying principles of whatever problem I am dealing with, allowing me to gain a working knowledge without getting bogged down in the details. It is this ability to be something of a jack-of-all trades (or a technical general practitioner as I prefer to think of it) that makes me valuable to the employer. Physics is the ideal background for this. In fact, as one goes up the management chain of this company, one finds that it is physics-heavy, as these are the people who have the ability to grasp the underlying concepts of a problem- which is what I think physics is all about. Hold the line when it comes to those things that traditionally make HMC great. That I was taught in small classes entirely by English-speaking PhD's who actually had office hours and didn't treat us an annoyance stands in stark contrast to the undergraduate experience of most of my peers.

I would say, using myself as an example, having a Physics background is a tremendous asset no matter what field one decides to go into. I really think that the problem solving skills I learned as a Physics major have helped me in my Engineering work. Also, since Physics is so fundamental to everything else (perhaps my view here is a little jaded?) there is no way to go wrong by learning Physics first and then moving up to other disciplines. ('Up' in the sense that 'C' is a higher level language than 'assembly'.) And now seems to be a great time for well-skilled scientists here in the Silicon Valley. The group I am in at IBM is concerned with magnetic disk media and most of the PhD's are from Physics/Material Science backgrounds.

Physics majors can certainly go on to do all kinds of strange things, even public policy and international affairs:

https://elliott.gwu.edu/pace

Physics training has been an invaluable aid throughout my career despite my grade in quantum mechanics. : >