As we've discussed before, Google has been planning an unavailable_after tag that would enable webmasters to alert Google to when content should no longer be crawled by the Googlebot. A Google Blog post by Dan Crow announces that this feature is now live. Additionally, Google is now accepting a META tag to be associated with any file. This allows webmasters to control access to PDFs, graphics, video, and audio files.
WebmasterWorld members are glad that Google is embracing additions to the robots.txt protocol, but they're concerned that other search engines won't follow suit. This is great for Google, but webmasters still need to be in control over the META elements as before for Yahoo, Ask, and MSN.