1. Upgrade grails.
2. Attempt a compile.
3. Uncomment all of the maven update locations in buildconfig.groovy
3. Uninstall each plugin that failed. Note, you don't use a script to uninstall the plugin, you need to remove the plugin entry from the application.properties file in the in your application's root directory.
4. Install the new plugin. Again no script, you create an entry in the buildconfig.groovy file.
(By the way if you use the script to try to install/remove a plugin, it does give you instructions about the new way to get them to work.)
5. Guess what, scaffolding is now a plugin, so you'll need to add it if you want any scaffolded controllers to work.
(Its good practice to run the clean script between each step to save you some greif.)
The good news is my other application only took 3 minutes to upgrade once I knew what I was doing.
I'm sorry that I don't have any examples of the changes that I made. I'm not near my work computer right now. I'll try and add some later.