On Friday, we reported on the new Google Sitelinks Search box - read that first if you missed it.
One new tidbit that I am glad Google's Pierre Far confirmed and I am incredibly upset the SEO space assumed incorrectly (at least some) was that adding the scheme markup 100% does not guarantee your site for having the new Sitelinks Searchbox feature.
Pierre Far from Google explained on Google+ minutes ago:
The question is: would adding the schema.org markup guarantee a site getting the search box?
The answer is no. It's a bit more nuanced (and clever) than that.
Pierre also shared another tidbit:
Bonus question on my previous G+ thread: Will adding a tracking parameter to URL pattern upset this at all?
Answer: not at all! But, as you're adding more complexity to your URL pattern, double and triple check it works correctly.
Finally, I do not believe Google won't show the search box if you do not add the schema, Google will still show it if they want to. The only thing it won't automatically do is redirect the search results to your site. Update, Google confirmed this.
Forum discussion at Google+.