A handful of quartz filters for saving PDFs.

As an example, using a 73 MB PDF from a 55 page Powerpoint presentation, the compressed files have the following sizes :
+ 75 dpi low quality : 2.7 MB
+ 75 dpi average quality : 3.2 MB
+ 150 dpi low quality : 4.2 MB
+ 150 dpi average quality : 5.3 MB
+ 300 dpi low quality : 7.6 MB
+ 300 dpi average quality : 10.2 MB
+ 600 dpi low quality : 16.0 MB
+ 600 dpi average quality : 20.3 MB

https://github.com/joshcarr/Apple-Quartz-Filters