Certainly do. Decided about eight years ago, after fumbling with some integrals that I know I used to be able to handle, to get my maths skills back.

Being the sort of person that I am, I signed up for a Masters in Maths with the Open University. It was far more brutal than I had hoped. I'd call it a success in as much as five and a half years later I finished it. I'll never do any maths of interest or note to the professional maths community, but I hope they at least recognise the qualification :/

Exams are a kid's game, I learned; three hours in an exam hall with a brutal set of maths questions is physically exhausting as well as mentally. There were five of those. Fully five-sixths of the MMaths with the OU is (or was, when I did it) assessed purely on formal exams in big exam halls, which is the only way it can be, but it sure does pile on the pressure with the whole year's worth of study riding on those three hours.

It taught me how to pick up a thick, savage maths text book and learn from it, which is a really useful ability. It also taught me to hate with a vengeance textbooks and explanations that don't clearly define their terms, their operations and their ranges of applicability. I read Physics at university the first time round, which was short on computing lectures as you might expect, so my introduction to order notation was formal and mathematical; the last time someone asked me about it in an interview, they got diagrams, graphs, ranges of applicability, definitions, examples, a short diatribe about how using the symbol '=' was really unhelpful, the whole lot. Seemed to go well; when we got to the section on his "things to ask about" sheet marked "communication skills" he just put a tick in the box and said we could skip over it, so one unexpected benefit of maths as a hobby has been to force my own mathematical thinking into rigour, with a knock-on effect in technical communication.

How it works for me is probably not how it would work for everyone, and I learned it the hard way; grind. Hour after hour, evening after evening, weekend after weekend of just sitting at the table with the book, some pencils and pads of paper. Each time I'd be done for the day, I'd pick up and recycle the drifts of paper that had collected on the floor as I'd discarded each piece I didn't need anymore. It gets in you, sometimes. I'd sit down at lunchtime with a sandwich, thinking I'd just look at the next question to get a feel for it, and get up again six hours later having thrashed it to death, picked it apart, textbooks I didn't even remember fetching from the shelf open on the desk, and pages and pages around my feet containing my own handwriting that I also didn't remember writing. Each time I found something I just couldn't grasp, couldn't understand, I'd just push on. Sometimes I'd never get it, sometimes I'd come back to it twenty pages later and it would seem simple (and sometimes I'd rage at how poorly the author had explained it, which was probably fifty percent the thrashing of my dying ego).

I have genuinely described as "black magic" taking a converging infinite series, and by adding zero to it, making it converge faster. So much faster.