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...we are now treating the 410 HTTP result code as a bit "more permanent" than a 404. So if you're absolutely sure that a page no longer exists and will never exist again, using a 410 would likely be a good thing...
In the worst case, the 410 will be treated the same as a 404; in the best case it'll be a bit quicker & stickier.
Google's Help Forum [google.com]
So, what does "quicker and stickier" mean? I would guess that a 410 will result in more rapidly lowered spidering of the url, and dropping the url from Google's search results. Naturally there would be some safeguards in place to protect webmasters against user error.
Hat tip to SE Roundtable [seroundtable.com]
I agree that they mean that 410ed URLs will be dropped faster and subsequently spidered less often, although I imagine that they *will* still spider them occasionally if they continue to find links to those URLs -- and especially from within the same domain (so we Webmasters need to be sure not to leave any orphan links behind on our own sites pointing to those 410ed URLs).
If there are no links at all to the 410ed URLs, I'd expect (hope) them to disappear fast and only rarely get spidered again -- if ever.
So the main question in my mind is, what happens if there are no on-site links to the 410ed URLs, but there *are* some third-party links to them? That's the grey area, and I'd guess that the URLs will still get spidered occasionally -- but *how* occasionally is the question...
I understand that Google has to deal with (probably a majority of) sites that don't use 410s, and many that use them incorrectly. But I'm glad to see the balance tipping a bit in favor of those sites that say "410-Gone" only when we really mean "It's gone, gone for good, it ain't never coming back, but if it ever does you'll see one or more *new* links to it appear on this domain."
The discussion in the cited thread got a bit heated and a bit confusing, so for those who read that thread and came away with some uncertainty, I'd recommend the following responses for URLs that are removed:
To generate a 410-Gone response, you'll need to use mod_alias or mod_rewrite in a .htaccess file or server config file on Apache, ISAPI Rewrite on IIS, or use a PHP or .asp script, etc.
As with any tweaking of server responses, it's a very good idea to check your work using a reliable server headers checker, and to be sure that the URL request returns the expected server status code directly, with no intervening 301, 302, or 303 redirects, for example. As usual, I recommend the "Live HTTP Headers" add-on for Firefox/Mozilla browsers as basic Webmaster kit.
If you can't generate a 410-Gone due to hosting restrictions or lack of necessary technical knowledge, then letting the URL go 404 and using Webmaster Tools very, very carefully to request removal is a still-viable approach. But before using the Removal Tool, it'd probably be a good idea to read the several "Help, I just accidentally removed my whole site!" threads here, and to be very sure that you understand exactly how the prefix-matching used by such tools works...
Where there is a risk that more than the desired single obsolete URL might be removed due to the Removal Tool's prefix-matching on 'common URL-paths,' a short-delay (instant) meta-refresh to a replacement URL may be a viable last resort if such a relevant replacement URL exists. To my knowledge, only Yahoo! has ever described how they handle this as a 301, but I haven't (re-)researched it recently. At the least, this might help Google 'figure it out' even if the unambiguous server response and Removal Tool options aren't possible.
Anyway, it'll be interesting to see how the newly-described Google 410 behavior plays out... :)