I've been doing this with plugins, and it's really useful stuff because you don't need be attached to the IIS process.
This tutorial explain how to do that locally: http://athulmt.blogspot.it/2012/09/debugging-plugin-in-crm-2011.html
Now I'm trying to debug CRM 2011 activity workflows with the plugin registration tool, but didn't find any way to do that because I don't know workflows.