I’ve mentioned it in passing in another post today, but it deserves a post of its own: Aaron Harnly has released MailPluginManager, a clever little plugin manager for Mail.app that can “inspect, enable, disable, install, and remove any plugin”.
Aaron says that he is willing to make the plugin manager available for other developers to include with their plugins, so that, as he hopes, “.mailbundle can become a first-class citizen”.
The plugin does a good job, although for some reason it doesn’t like the look of Mail Act-on:
You can find MailPluginManager in the most recent Letterbox public beta 
, although you don’t need to use Letterbox to get its benefits. It is a free-standing app.
I’m having trouble getting mail.appetizer to work using the plugin manager (or at all actually). Can anyone help me out?
@John, Mail.appetizer is not working too well under Leopard at the moment, although you can try your luck following the instructions in this post:
http://www.hawkwings.net/2007/10/30/leopards-mails-mailapp-and-plugins-trial-and-error/
how do you open the plugin manager when not installing an app?