To allow tethering to Canon and Nikon cameras Capture One uses an SDK provided by Canon to Phase One. Canon did not update their SDK after the release of OSX Leopard (OSX 10.5) and that SDK was found to be unstable when used with later versions of OSX 10.5 and all versions of OSX Snow Leopard OSX 10.6.
This lead to a lot of very unhappy Canon users when tethering to Capture One 5 Pro. The most common problem was that during fast shooting Capture One would hang (“beach ball”) – sometimes for several minutes at a time*.
Canon has finally revised their SDK for full compatibility/stability in OSX Leopard and Snow Leopard and that SDK is used in Capture One 6 Pro as well as Lightroom 3.
In other words: Canon shooters rejoice – your days of Capture One hanging when rapidly shooting tethered to C1 are over!
*An advanced user could open up OSX Activity Monitor and see that the thread that was non-responsive was actually the Canon SDK and not Capture One. By force quitting the Canon SDK the camera connection would be dropped and reacquired and the shoot could continue.