Spotlight is pretty awesome imo. I had problems on previous versions, but that was specific to a corrupt PDF. Stuff like spotlight comments enhances it further. I search something like 25k docs in various formats on my Mac in seconds.
Windows is far worse. They don't have a native PDF search facility (at least on Windows 7) and its sloooow.
iOS, I agree. It's gotten better, but the app search thing is bizarre -- especially since it works so well on Mac.