I've fleshed out ditz's plugin architecture and just added a plugin that ties it more closely to git. With this plugin enabled, you can tie issues to feature branches and automatically get a list of commits on that branch (until they're merged into master, at which point that becomes impossible, thanks to the magic of git).
Here's an example: Sup's configurable colors issue.
With these changes, Ditz is now firmly in the MVC camp. The models are created from yaml objects on disk; the views are an HTML renderer (using ERB) and a screen renderer (using puts technology), and the controller is the previously-mentioned operator.rb.
If you look at the plugin code you see that it need to modify all three of these components. It adds fields to the Issue and Config objects, it adds output to the HTML and screen views, and it adds commands to the controller. The fact that it can do this in a few lines of code is pretty sweet.