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Google is now sending webmasters notifications of the new Sitelinks search box functionality that we covered here not just two or three times but this would be the forth.
The notifications are coming via Google Webmaster Tools message center, asking webmasters to "make your site ready for the new sitelinks search box."
Wissam Dandan, and many others, posted screen shots of the message on Google+. Here is a copy:
Did you get one of these?
Forum discussion at Google+.
