I've placed a small shell script at:

http://www-mtl.mit.edu/~mcmahill/netbsd/make_patches

Its job is to make the creation of patches for a package easier.
Basically the procedure is:

when creating a new package, as you find files which need patching, 
% cp oldfile oldfile.orig
and make your changes.

When the program compiles and runs as desired, cd to ${WRKSRC} and

% make_patches

This searches for all the *.orig files and runs 'diff' to create patches
which are stored in ../../patches/patch-##.  Also, the $NetBSD$ header is
stuck at the top of each patch file.

Its pretty simple, its not very pretty, but its a time saver if you need
to create 20 different patch files.

hope this is mildly useful to someone else too....

-Dan