Generally the CBM ports were meant to connect new space station nodes together.
The nadir port on Harmony (Node 2) has been used for more berthings than any other that I am aware of.
As of Jan 2014, it has supported:
- 4 HTV berthings (plus one swap of the HTV from nadir to zenith to make room for a space shuttle docking) for a total of 5.
- 3 Dragon berthings (#4 due in Feb 2014)
- 2 Cygnus berthings
For a total of ten berthing events to date of writing this question, with 16 more expected at a minimum (duration of Orbital (8 flight) and SpaceX's (12 flights) current contracts with NASA).
What is the operational lifetime, in units of berthing events for a CBM port on an ISS module?
Contrast with the aft port of Zvezda which has supported dozens of docking operations, but is of a very different design. Or the forward port on Mir. Or aft port on Kvant which was attached to the aft port of Mir).