pageoneresults - 1:19 pm on Feb 1, 2011 (gmt 0)
Very few sites use the 410 response code. If I recall correctly, Google has said that they don't treat it any differently from a 404.
I might have to disagree with that. Google appears to handle 410 Gone exactly as it says on the tin. I've implemented it recently and have seen pages "Gone" within 24-48 hours.
I'm sure there are others who will chime in with similar findings. If a document does not exist anymore and there is no viable replacement for a 301, then 410 Gone is the suggested server response. A 404 is too vague and Googlebot will continue to request the document forever as long as there are external links to it.
This is where finite error reporting comes into play. You should have few, if any 404s. At some point, you'll capture those repetitive 404s and redirect them to an appropriate document. If no replacement exists, drop a 410 Gone in there.
I'd like to point out that a 410 Gone is probably your last resort. You'll want to preserve whatever equity may have been associated with the document that no longer exists, especially if there are inbound links that you have little to no control over. You'll of course 301 in this instance to the most appropriate document.
Note: I was surprised when I did the 410 implementation a little while back. Within 24-48 hours Google removed those pages from its index, it acted just like a URL Removal request without all the paperwork. :)