Google has been displaying site links - the linked words below a main search result that leads to internal pages of that website - for some time now. But there has been a restructuring. Now, instead of the stacked appearance of several links, in several columns, more sitelinks are being seen on one line, just four across at the bottom of the result. As such, you can expect to see more results on the results page, as there will be more room. But the ramifications don't stop there.
For advertisers, it's possible that paid links will become more prominent in the eyes of users. When sitelinks are stacked, it could be argued that attention is drawn to the larger real estate that the result inhabits, thus garnering more attention - and clicks - away from smaller paid ads. The larger sitelink sections might even be confused with ads themselves, as they simply look different than regular results. So, one could theoretically see a rise in clicks on PPC search ads, which could result in a more competitive landscape, or more opportunities for advertisers.
It also means that as a site owner, you need to pay close attention to how your sitelinks are being displayed within search results. In the past, one would see upwards of eight sitelinks, where now there seem to be no more than four. That means the choices for users are fewer, and so is your opportunity to capture a Web surfer. While there are no official guidelines or rules as to how Google displays sitelinks, some correlations can be found. Anchor text, page navigation, meta tags, even ALT tag text have been rumored and seen to show up in sitelinks. This means that internal navigation is a key element to how (and whether) sitelinks show up in your search results. Like most things Google, we don't know for sure, but it is a reminder to optimize these elements of your website.
For now, it appears that the change is not sweeping - some results still show the older version of sitelinks and some results are using the new system. Google will continue to test and tweak, so keep a close eye out for developments.