looking back, what aspects of your Ph.D. training do you find most useful now? was it deep expertise in one particular sub-field? was it a certain type of work ethic or approach to problems? was it the doors it opened for you professionally? etc.
The field certainly helped. I worked in databases, data structures and algorithms, and the exposure to those ideas has been a huge benefit since I'm still working in those areas. I'm constantly surprised at how things that are just intuitively obvious to me are alien to many others. Grad school is when much of that intuition was absorbed, I think.
I think that "work ethic" (mine, at least) is just hardwired. Same for approach to problems. I wouldn't say that grad school influenced these so much as help me realize what they were. I actually goofed off quite a bit in grad school. My work ethic (as in long hours, and job above all else) wasn't tested until I joined my first startup.
Opening doors: not so much. My thesis adviser was not in the mainstream of our field, and most of my friends were in other fields. My professional contacts started developing when I joined my first startup. I was extremely lucky at this startup in three ways: 1) working with world-class engineers, 2) in a well-conceived and well-funded startup, and 3) they were willing to take me, an academic who actually liked writing software, and give me a chance.
Having a PhD was a potential problem early on. I tried teaching/research after grad school, and discovered that it wasn't for me. (This may have been the transition from a Canadian school with easy access to small amounts of funding, to a grant-writing powerhouse in the US, where professors seemed to spend all of their time pursuing grants.) I was lucky in my transition to the software industry -- I have friends who wanted to make that transition and were not able to. And in fact, at my first startup, there was vague suspicion of me just for having the degree. But now, years later, I think that it was time well spent, better probably than what I'd get out of the usual first jobs after college.
Another thing to keep in mind is what sort of PhD you do. A highly theoretical focus is rarely good preparation for life in the software industry. A highly applied focus is great preparation, (I'm thinking of the long list of developers who have come out of UC Berkeley, and of course, there are the google founders.)
