The full version of this announcement is available.
Since Kris has just announced a new version of XY-pic, allow me to offer up my own diagram package for users of dvips.
The macros in kuvio.tex use PostScript embedded in \special control sequences to rotate arrows from the horizontal.
For anyone who's interested, the following files can be found.
See the full version of this announcement for a summary of the main features of the macros in kuvio.tex and of the contents of the files listed above.