I don't believe that there are grunt plugins for full spectrum of tasks needed to build and deploy all aspects of an AEM project. If you read excellent blog post Scott pointed to from Citytech you'll see that they are using Grunt to do common JavaScript and CSS tasks (including integration to running author instances). Where you'll still need to look to Maven are the more Java related tasks like building and compiling an OSGI bundle for example. There are a lot of tasks in between those two items, so I think the key is to come up with the right tools for the right tasks and then combine them together to get the most productivity from your development teams.