Thanks to this PDF Hacks excerpt, I learned of pdftk, the PDF Toolkit. It is in the FreeBSD ports tree. I used it like this:
janney:/home/richard$ pdftk *.pdf cat output nso_netdiagrams.pdf
janney:/home/richard$ ls -al nso_netdiagrams.pdf
-rw-r--r-- 1 richard richard 824385 Dec 11 11:00 nso_netdiagrams.pdf
That's it. When I was done, all of the .pdf in the directory were assembled into the single nso_netdiagrams.pdf. Incidentally, I print my .ppt slides directly to .pdf using the free PDFCreator. I know OpenOffice.org also supports this, but I prefer PowerPoint.