My first post for ages! Sorry about that....
Something quite exciting, that I've had a crack at fixing myself, but the combination of my poor java and python skills has prevented me from completing this adequately. However, the combined skills of the trac developers and the development team for Mylyn and the Mylyn Trac connector have managed to combine to finally provide the highly awaited Mylyn, Eclipse and custom Trac workflow integration!
That's right! If you have custom workflows and actions specified on Trac, you can now managed tickets directly in eclipse with Mylyn tasks.
In order to get this working you will need to export the latest trunk of the TracXMLRPC (current at time of writing at r6058 plugin from Trac-Hacks and install it on your trac server. (Installation is easy - command line, change to the top level of the TracXMLRPC export folder, run the command "python setup.py install", restart apache, done)
Having installed the updated XMLRPC plugin you'll also need to update Mylyn in eclipse to the latest weekly of Mylyn and the Trac Connector. Just add the update sites to the software update section in eclipse and use them to do an update. Current version at time of writing is : 3.2.0I20090616-0200-e3x.
When you restart eclipse you should be all sorted! Custom action in Mylyn tasks in Eclipse! One thing to note. Mylyn caches the UI elements, so when you open a task that you've previously openned you may need to hit the "refresh" button at the top to load the custom actions. Other than that it all looks fine.
One last note.... Both the TracXMLRPC plugin and the Mylyn plugin and Trac Connector are all trunk level releases, so the standard "Here be dragons" disclaimer applies. If you find any problems, please make sure you report them to the right people on the appropriate forum.