Being in Oxford has made me think about one of the turning points in my life, which came when I finished my undergraduate degree. Having had a traumatic honours year, I took the course of least resistance and enrolled in a PhD at the same university, with the same supervisor I had had for my honours thesis. That went nowhere — eventually I abandoned it entirely — and also served to put me off academia.
In retrospect, it would have made more sense for me to go overseas to do a PhD, or if not a full PhD then something like the one year Cambridge Tripos (now the Certificate of Advanced Study in Mathematics), which is what my friend Sean did. Getting out of the country would have been good for me personally, as well as better academically.
My subsequent life would probably have been very different. I might have ended up as an academic, or working in finance like so many of my friends did, rather than in practical IT. On the other hand, while I ended up with a job as a Unix and then Linux sysadmin more or less by accident — Bernard happened to come by the Madsen canteen with a job offer — my interest in systems was already quite strong. (Which reminds me how much I miss David Hogan.)
Anyway, I have no regrets. I just don't think that way about the past, and biographical counterfactuals are always speculative — I could also have been hit and killed by a bus a week after leaving Australia.
Would I ever consider having another go at a PhD? Possibly, but my interests are now so broad it would be hard to narrow my focus for three or four years.