If you read the TAC instructions for authors, you will find that we discourage the use of the graphics package unless absolutely necessary because, for the time being, dvi is still our basic archive format and graphics specials were not rendered properly by dvi viewers. I recently discovered that at least one dvi viewer does indeed render graphics specials. Namely the yap viewer that comes with miktex, a windows-specific implementation of tex enters something called dvips mode (meaning, I imagine, an on-the fly conversion to ps and then rendering that). To be more precise, miktex2.5 asks if you want dvips mode (why wouldn't you?) and miktex2.7 enters it automatically. (I don't know about 2.6). As far as I know no Unix (or Linux) viewer does this. Neither pdflatex nor dvipdfm renders graphics specials correctly. The only way I have been able to get correct pdf files is to first use dvips to make a ps file and then use ghostscript to convert to pdf. Still, one can hope that these problems will disappear in some future implementations and we may withdraw our objections to the use of the graphics package. At that point, our reluctance to use Paul Taylor's diagrams will also disappear. For the time being, however, we will continue to recommend the use of xy-pic and, in particular, the diagxy front end.