Answer Highlighting in short basically uses Google Squared technology to highlight in the search snippet the answer to your search query. For example, and I don't see this in the live Google results right now, if you search for [empire state height], in the past (current) you would have seen this:
With the enhancement, you would see the answer:
Getting the answer in the search results, is a goal of Google, but that means, or can mean, less click throughs from Google to your web site. Webmasters often live off traffic and conversions, so this can be a bit upsetting to many webmasters.
Brett Tabke said in a WebmasterWorld thread:
Taking another page out of the WolframAlpha play book, Google introduces Serps with answers. You may never need to visit any site again.
The other enhancement is allowing event data in rich snippets. How does that improve the feature? Just look at this snippet:
Forum discussion at WebmasterWorld.