View Factor was the first to announce a USB follow focus for Canon HDSLR cameras. Overcoming the challenges of Canon’s USB focus control has proven to be a huge undertaking. Their original projection was late summer 2010, but that seems to have been pushed back.
It looks like another person has taken on the endeavor of building a USB follow focus. They look to be in the manufacturing phase. Hopefully we will see working model soon.
Read more on Cinema5D’s forums.
[UPDATE] Curt from View Factor contacted us via email with an update to their USB follow focus:
We have been working diligently on our solution and will be announcing more information shortly.