The PhD has helped in a few ways:
- I've been doing database-related startups for 20+ years, and my deep understanding of database technology has proven very useful. I could have gained some of this insight by working, but I think this path has led to a broader and stronger foundation.
- On a couple of projects, my actual dissertation subject has been relevant.
- While a PhD was off-putting to employers at my first startup (understandable, since it was also my first actual software job, and they had no evidence that I actually wanted to write software and was capable of doing so); once I got past that, the title was occasionally a useful thing to put out there. (On one occasion, I was asked to write a paper for an industry group with "lots of symbols".)
- Contacts with the academic world of databases that have come in handy over the years.