Google has added a meta tag that allows the expiration date for an entry to be automatically propagated to the search engine. Using this tag will cause a page to be hidden from the Google search results on its expiration date.
Of course, most pages don’t have an expiration date, but when it is used it’s really useful to have the page automatically removed from Google’s index. Otherwise people may find the page through Google, but end up on your site’s “not-found” page - or something even worse, depending on the quality of your templates.
To exploit this feature in your templates (and I see no reason why you shouldn’t), add the following line within the <head> section of the template, within the scope of the exp:weblog:entries tag:
{if expiration_date}<meta name="googlebot" content="unavailable_after: {expiration_date format="{DATE_RFC850}"}">{/if}More information is available on the Official Google Blog.