Using Print » PDF » Save PDF as PostScript appears to result in substantially smaller files than using Print » PDF » Save as PDF, assuming you have Adobe Acrobat (or other similar tool; I used V7 of Acrobat) installed to convert the resultant PostScript file to a PDF. I reached this conclusion after testing a document of my own: a 29MB document in Pages, which was mostly text with some graphics and photos. My goal was a compact email-friendly version, less than 1MB.
Print » PDF » Save as PDF yielded a file 60MB in size, and after several lengthy operations, the best Acrobat could squeeze it down to was 3MB. Using Print » PDF » Save PDF as PostScript produced a 48MB PS file. From this, Preview generated a 75MB file, but Acrobat produced a file of just 1.2MB, before optimisation. Selecting File » Reduce File Size brought this down further to 900KB, with no discernible loss of quality in photos or graphics.
I'm sure this is common knowledge to those who do this kind of thing on a daily basis, but for those who don't, it may be useful. I really like using Pages to produce high quality documents, but the problem comes when sharing them with Windows users, and PDF is obviously ideal for this. It's just a shame Pages can't deliver a compact file itself.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070130202440991