I opened it, dragged my PDF file onto its windowm and then clicked the button labeled Create PDF. Guess what? The generated PDF was much smaller. I've got no idea whether it is as effecient as other tools or not, but the result was great for my particular file: 1.69MB was reduced to 289KB.
Starting now, you can use PDFLab to shrink PDF files, freely.
[robg adds: You can also use the ColorSync Utility, in the Utilities folder, to do this.]

