Google announced a new, smaller version of their sitelinks search feature on their official Webmaster Blog today. The new mini-sitelinks will appear on more than just the top search result, and will occupy a maximum of one line and four links per result. Sitelinks were originally added by Google to help people jump to more specific portions of large web domains like Amazon or About.com. Additionally, the original version of sitelinks ws only generated for the top-most result of a search query; the new one-liners can appear on other results on the first page.
Sitelinks can be seen as a slow encroachment of Google into a function that is traditionally part of the experience of visiting a site. Depending on how a site is structured, a business might not appreciate customers being pushed directly to a page below the front page. It could be seen as taking away from the customer's average time on site (a commonly measured site statistic) as well as potentially confusing if a company's offerings are complex and require some explanation.
To this end, Google has made available settings in its suite of Google Webmaster Tools that allow domain holders, once registered, to block specific sitelinks from being listed in Google search results. It does appear that the block is only temporary (90 days) and for specific pages - which means webmasters are going to have a headache dealing with it if they have a lot of potential sitelink pages to block. In any case, Google has written about how to block sitelinks here.