I discovered this and posted it on my blog but, but the more I dug the more interesting it seems to get. To prevent the eventual Threadjacking™ I'll share it here. Phrasing your query as a natural language question seems to trigger some special programming, see links to SERP's below.
Want some incentive that should start optimizing for definitions look at the SERP for [what is a reverse mortgage] see how being the #1 organic SERP simply isn't enough anymore (I get 3 ads, 1 definition, and 1 news result before I get any organic results).
Lastly Matt commented this was a UI test on his blog last year so I guess it's something they are going forward with and SEO's should start paying attention to.