I am running Photo Mechanic version 5 and 4.6.9 (I search with both version and the same problem) and I run Mac OS X 10.8.2 on my Intel-based Mac. I don´t know why, but it seems like IPTC data aren´t recognized: only filename. I have tried to search in "quick search" and with Edit->Search, and no results.
Thanks, Manuvui