My lifetime total for caps that didn't seal sufficiently is 1, so far.
I opened one, it was totally flat. So I just dumped it out and got another. It may have been a Bass or Warsteiner bottle: I know that I have some of both in my rotation, and I agree with whoever recently posted that they are harder to get a good seal on.
Bottle conditioning: Robust Porter
Drinking: Saison Dupont clone, tripel
Coming soon: Columbus APA, Rich Red ale