Mac OS X Lion: save as PDF-X

1. Open /Applications/Utilities/ColorSync.app, Select Filters, click the triangle to the right of the "Create Generic PDFX-3 Document" filter
   
2. Select "Duplicate Filter"
   
3. Open the new "Create Generic PDFX-3 Document Copy" filter, then "Domains", tick "PDF Workflows"
   
4. Now when printing, you can click "PDF" button
   
   then select "Create Generic PDFX-3 Document Copy.qfilter" to create (or save as) PDFX-3 document.