This was interesting. I've been regretting for a while that I didn't suck it up and learn more math in college (the first time). Hindsight being what it is, though, it's hard for me to be too upset about it. If I had been a more dedicated student - and less a dedicated hedonist - I'd have gotten that Math\Comp Sci degree instead of the English degree. I would likely have gotten a job in Atlanta instead of moving back to Tennessee and meeting my wife-to-be working in a restaurant.
So, being thoroughly happy with my life, it's hard for me to have much regret for anything I didn't do that might have put me on a different path to today.
Still, I've always had it in the back of my mind that if I found myself financially secure I'd go back to school and learn all the math I skipped back in the day.