I helped someone with this question and it took a few tries for me to find the answer. Here's the question:

"How do I create a smaller pdf from iWork. When I try I get 12MB files and I used to know a way to shrink them down without much noticeable decrease in screen resolution".

I managed to find the answer and here it is for the curious:

1. From within Pages or any other application you're creating a PDF from, click on "Print" in the File pull-down menu.
2. In the Print dialog box, click on the third pull-down menu box ("Copies and Pages"). Select "ColorSync" from the pull-down menu.
3. Click on the "Quartz Filter" button and select "Reduce File Size."
4. Click "Save as PDF"

Or if you have Acrobat, you can simply open the file and re-save over the top of it, vastly reduces the file size

The person didn't have Acrobat.

Thanks for the tip. Is there any downside (e.g., loss of printing quality) to this compression?

I would assume so.