When you put a size threshold on font smoothing and make the text smaller than that, at least in Safari, you do appear to get the full TrueType hinting, not the subtler antialiased-font hinting. But the font metrics are not the metrics associated with the fully hinted font but the same metrics used for the antialiased font, so the spacing looks slightly drunken and cramped (it's the inverse of the problem I mentioned in my old MacEdition article, in which some old apps were using metrics with full TrueType hinting but Quartz antialiased rendering).
But the difference between the letterforms with and without antialiasing is not as great as I expected, and perhaps not as great as it used to be in early Mac OS X revs. It might be that Apple's modern font renderer is paying attention to the TrueType hint bytecodes when hinting for antialiased rendering, but just using a slightly more relaxed algorithm for grid-fitting. If so, they're being very clever.
But the difference between the letterforms with and without antialiasing is not as great as I expected, and perhaps not as great as it used to be in early Mac OS X revs. It might be that Apple's modern font renderer is paying attention to the TrueType hint bytecodes when hinting for antialiased rendering, but just using a slightly more relaxed algorithm for grid-fitting. If so, they're being very clever.