Host
Device            iBook            Mac Pro

My CF reader
  1GB card        works            FAILS
  2GB card        works            FAILS
Jon's CF reader
  1GB card        FAILS            FAILS
  2GB card
Memory Stick                       works
Portable HDD      works            works
Keyboard                           works
Trackball                          works

This only describes recent tests.  My CF reader used to work with the
Mac Pro, and the keyboard and trackball worked on the iBook last time
I used them with it.

Choice of USB port on the Mac Pro (front/back) doesn't make a
difference.

The logging USB driver displays different log trace from my and Jon's
CF reader, on the Mac Pro.  I can't remember details but Jon's
produced some errors about protocol violation followed by a stop while
mine produced a constant stream of messages (that I don't recall the
details of).