How to monitor file access for an OS X application?
Solution 1:
Instruments—a part of the Apple Xcode development suite—can monitor all file access and writes. Open it from /Applications/Xcode.app/Contents/Applications/Instruments.app, select your application or process, and press Start. You have extensive filter options available in the menus.
Older versions of Xcode are storing the App at /Developer/Applications/Instruments.app
Solution 2:
There is the command opensnoop. Run without arguments, it may overwhelm you with output, but it can be run with arguments -n name to limit output to processes named name.