In my case, I see errors and lots of them:
error: '::FlushVol' has not been declared
error: 'HideCursor' was not declared in this scope
error: 'ShowCursor' was not declared in this scope
error: 'LMGetFractEnable' was not declared in this scope
error: 'GetOutlinePreferred' was not declared in this scope
error: 'GetPreserveGlyph' was not declared in this scope
error: 'GetWindowEventTarget' was not declared in this scope
error: 'SetFractEnable' was not declared in this scope
error: 'SetOutlinePreferred' was not declared in this scope
error: 'MoveWindow' was not declared in this scope
error: 'SetOutlinePreferred' was not declared in this scope
error: 'OpenCPicture' was not declared in this scope
error: 'SetControlPopupMenuHandle' was not declared in this scope
error: '::SetControlMaximum' has not been declared
error: '::DrawThemeMenuItem' has not been declared
error: 'GetIntlResource' was not declared in this scope
error: 'CompareString' was not declared in this scope
error: '::SetMenuWidth' has not been declared
error: 'IsWindowVisible' was not declared in this scope
error: '::GetPicture' has not been declared
error: '::DrawPicture' has not been declared
error: '::EraseRect' has not been declared
error: '::FindDialogItem' has not been declared
.... lots more errors ...
So, we have a litany straight out of Inside Macintosh Vol. 1-3: all of QuickDraw, much of the File Manager, the Control Manager, the Dialog Manager, the Window Manager, the Menu Manager, the Font Manager all gone, but surprisingly not the Resource Manager. Anything that uses Pascal strings or FSSpecs. Few of the API's which came from the Classic Mac OS survive a 64 bit compile.
I don't know in the short term, what the carrot is for getting independent developers to make 64-bit compiles. Unless you are doing something that really needs 6 GB of real RAM—very few applications—there seems to be little performance advantage for 64-bit. And, it's hard taking a Carbon application, ripping out the APIs behind its entire GUI, and putting it back together again. Lots of redesign and drudgery for little immediate payoff. In the long term, Apple will presumably stop supporting 32-bit applications, but that is in the very long term.
Plus, there are little bits of functionality in the Carbon APIs which are hard to replicate in the more modern APIs. One example is embedding one's private metadata in the PICT clipboard flavor. I'd very much like to know how to do that with the PDF API. Another example is the XOR drawing mode for doing tracking, stupid and old fashioned, yes, hard to replace, yes.
There's an Ars Technica article which goes into this in more detail.
