I had a brief but influential (for me: I'm sure he quickly forgot it) correspondence with the philosopher-of-science Paul Feyerabend when I was 19.
I sent him a philosophical manuscript of mine, printed on a crappy dot matrix printer ... I think it was called "Lies and False Truths." I asked him to read it, and also asked his advice on where I should go to grad school to study philosophy. I was in the middle of my second year of grad school, working toward my PhD in math, but I was having second thoughts about math as a career....
He replied with a densely written postcard, saying he wasn't going to read my book because he was spending most of his time on non-philosophy pursuits ... but that he'd glanced it over and it looked creative and interesting (or something like that: I forget the exact words) ... and, most usefully, telling me that if I wanted to be a real philosopher I should not study philosophy academically nor become a philosophy professor, but should study science and/or arts and then pursue philosophy independently.
His advice struck the right chord and the temporary insanity that had caused me to briefly consider becoming a professional philosopher, vanished into the mysterious fog from which it had emerged ...
(I think there may have been another couple brief letters back and forth too, not sure...)
(I had third thoughts about math grad school about 6 months after that, and briefly moved to Vegas to become a telemarketer and Henry-Miller-meets-Nietzsche style prose-poem ranter ... but that's another story ... and anyways I went back to grad school and completed my PhD fairly expeditiously by age 22...)
Even at that absurdly young age (but even more so now), I had a lot of disagreements with Feyerabend's ideas on philosophy of science -- but I loved his contentious, informal-yet-rigorous, individualistic style. He thought for himself, not within any specific school of thought or tradition. That's why I wrote to him -- I viewed him as a sort of kindred maverick (if that word is still usable anymore, given what Maverick McCain has done to it ... heh ;-p)
My own current philosophy of science has very little to do with his, but, I'm sure we would have enjoyed arguing the issues together!
He basically argued that science was a social phenomenon with no fixed method. He gave lots of wonderful examples of how creative scientists had worked outside of any known methods.
While I think that's true, I don't think it's the most interesting observation one can make about science ... it seems to me there are some nice formal models you can posit that are good approximations explaining a lot about the social phenomenon of science, even though they're not complete explanations. The grungy details (in chronological order) are at: