Hmm. Just back from a podiatrist. It turns out that the reason my verruca didn't go away when I put verruca-ridding stuff on it was because it's a corn. That also explains why I couldn't figure out where I picked it up: it's a pressure-related problem, not a virus-related one.
But then came the bigger whammy. The man looked at my unusually-high arches (oft-commented upon by friends but never before mentioned by the medical profession), checked out the uneven wear on the soles of my shoes, and diagnosed a case of super-pronation.
He asked me whether I have achy feet in the mornings (check) and maybe back problems (check) and said I might want to look into getting myself a set of orthotic insoles.
It didn't click at the time, but I'm wondering if this might also go some way to explaining the foot problems I had at the beginning of the year -- the ones pushed out of my and the physiotherapist's mind after my snowboarding injury did more pressing things to my knee. At the time, my GP said my foot X-ray showed rather unusual wear, and that would be consistent with what this podiatrist just said.
So. I now have a sore toe that's been carved about a bit, a desire to get some new walking shoes soon, and the idea to go back after Christmas (when the orthotics lab he uses will be open again) and get myself fitted up, as it were.