Google has published a new latest Webmaster Help video, In that, Matt Cutts discusses how Google handles 404s versus how it handles 410s.
Whenever a browser request for a page, the web server sends back a status code,” he says. ’200 might mean everything went totally fine. 404 means the page was not found. 410 typically means ‘gone,’ as in the page is not found, and we do not expect it to come back. So 410 has a little more of a connotation that this page is permanently gone.