From a discussion on Twitter last night, I put together an API solution to export the name of every subcategory and material in a group of RFAs.
In this sample it is hard-coded to check every RFA in the C:\ProgramData\Autodesk\RAC 2013\Libraries\US Imperial\Doors folder. The output is written to individual files in the TEMP folder (one file for material info & one file for category info).
The source code is available in my Udemy course on the Revit API