I also wanted this ability for my Pivotal Tracker projects. So I wrote the needed integration code and released omnifocus-pivotaltracker. It syncs non-finished stories, tasks and chores that are assigned to you from all you Pivotal Tracker projects.
To start using it, simply install the gem and start sync:
$ gem install omnifocus-pivotaltracker $ of sync
On the first run the sync will create
~/.omnifocus-pivotaltracker.yml file. Edit it and fill your Pivotal Tracker name and token. After filling those, just re-run
of sync and it will do the first sync. After that you can run
of sync any time and it will update the OmniFocus data.