Matt Cutts: on 410's 404's Google, and SEO

Matt Cutts: Gadgets, Google, and SEO: "a good interview with the Sitemaps team. The most useful tidbit (which I didn�t know until now) is that Google treats a 404 HTTP status code (page not found, but it may reappear) and a 410 HTTP status code (page not found, and it�s gone forever) in the same way. I believe that we treat 404s as if they were 410s; once Googlebot has seen a 404 at that location, I think we assume that the document is gone forever. Given how many people use 404 instead of 410, that�s probably a good call for the time being."