> > [Chris]-- differences in the metrics (these can cause major
differences in
> > the typesetting).
> Yes, differences in the metrics, which can reshape the whole document.

Oh dear, yes!  This does rather mess-up fine typesetting.

My feeling is that since the fonts available are going to get more and
more diverse (if only very slowly) the robust medium-term solution for
a TeX-like typesetting engine is to add the ability to bundle the
font-metrics with the document (possibly virtually when network font
warehouses really exist).

This is analogical to putting the glyph information into a ps or pdf
form of a document.