I am running 10.8.2, and I just successfully inserted a PDF file into a new email, right clicked the file, selected view as Icon, and the PDF entire document shown in the email shrunk to an Icon. Mine works fine,
That said, I would suggest you reboot while simultaneously holding down the Command - R keys to boot into the Mountain Lion Recovery Partition. When there, enter Disk Utility and run "Repair Disk" from there on the Mac Hard Drive, and then run "Repair Permissions" twice. Then reboot into Mountain Lion's partition. That may help.
Hope this helps 🙂