It was wildly successful when it was rolled out, so now they are thinking of expanding it. It was a means of search like nothing that had been seen before at that time and that's why it was so successful. It was the simplest idea possible that came just at the right time, that's why it was the best means of in-depth search. It's "Sitelinks" from Google, the way to look under the hood of some
sites and reduce the number of clicks it would take you to get exactly where you want.
You might have noticed it before, I mean I'm sure you did, but you might have observed that it wasn't available for every site, only for the big ones. I'm talking about the links displayed directly under a search result queried on the page that sent you directly deeper down into the "belly of the beast", a.k.a. the site you were after. The previous number of such links was 4, nicely fit into a column that greedily awaited your clicks. Now, it's double the trouble, double the fun with an additional 4 other links that will be displayed. Plus that the number of sites that will benefit from this indexation will be greatly increased, or at least that's what papa Google says.
The usability of these links was circumstantial, in case you weren't quite sure what it was exactly that you were after, it was and from now on it will still be the best means to understand what such a site has to offer, because of the descriptive names that will be given further thought in.
What else could there be to say, it's an update that will most likely make your searching go even smoother, combined with the regional Google databases and datacenters that will direct and prioritize your queries, so that they don't have to suffer from Internet latency, the two of them together should give you the signal for extremely smooth sailing on the web. Or surfing. Or you get my point.