In eclipse 3.2, there is good support for keybindings, commands, and handlers. There are some snippets available at Platform Command Framework.
But it's not obvious how to link your command+handler implementation to a menu or toolbar item. The <action/> elements have a definitionId attribute that can link the action to a command, but that allows the action's IActionDelegate to be linked to the keybinding (through the command). It turns the action's IActionDelegate into a handler for keybinding purposes through the use of an ActionHandler proxy class.
But what if you would prefer to implement your commands and handlers, and then just have the command called from your menus the same way it is through keybindings.
As it turns out, there is public API that will allow you to create a GenericCommandActionDelegate. I have an example available on the Platform Command Framework page.
The implementation takes advantage of the fact that the action element is created through IConfigurationElement#createExecutableExtension(*), which means that your action delegate can implement IExecutableExtension and receive extra configuration information from the plugin.xml.
It's not a perfect solution for 3.2 (there would need to be more work to support something like checked state or radio buttons), but it will allow you to focus on creating command and handlers, and then using the action based extensions to execute your commands.
The same strategy could be used for 3.1 as well, although some modifications would have to be made. In 3.1, you have to build your own ExecutionEvent and call the Command#execute*(*) method yourself.