With migrating to yeoman 1.0 from version 0.9.6 you have to essentially create a new project and import your source over as the builds have changed so much. Check the documentation from yeoman on how to do the upgrade.
I have an Angularjs project with coffeescript that I wanted to have compile to individual js files. There are lots of good examples on how grunt works with coffeescript from the source https://github.com/roytruelove/angular-grunt-coffeescript
Purpose of compiling coffeescript this way.
This will create 1 js file per coffee file and have them sit next to the original source coffeescript file. This is not what you want to release to production as there are a lot of network requests per page.