Out of curiosity: The typical situation for ports tree forks will be that the master branch tracks macports-ports/origin/master while anything personal/custom will be kept in a personal branch.
How complicated would it be to set up the fork such that you can put custom ports in the default branch, and set up another branch to track the official ports tree? I have a hunch that it shouldn't be too hard to do in .git/config once you know exactly what to change. This would allow me to maintain a branch with my own ports (and possibly additional things like a README) and check out my fork on any of the 3+ machines where I want to deploy that customised port tree, while still being able to sync with the official ports tree. Thanks, R.