problem: how do you significantly compress large PDFs without adobe acrobat?

solution: use one of the following free scripts…

compress PDF workflow for 10.5
compress PDF workflow 6.0 for 10.6
the above provide the same functionality on 10.5 & 10.6 respectively as was present on 10.4 with ‘compress pdf’ in the ‘save as pdf’ section of the print dialogue. it is an automator workflow which gets installed in the following location:
‘/Library/PDF Services/Compress PDF.workflow’
the compression factor can be easily tweaked by opening the workflow in automator.

shrinkit by panic (check out their fantastic website)
this will be most effective on vectorised information, e.g. illustrator files.