I wonder how many people out there actually use Sitelinks in their Google Adwords campaign, I don't know the answer, but I can tell you that they are crazy not to. By pretty much any measure I have run across and my own experience, Adding appropriate sitelinks to a google adwords campaign can have a dramatically positive impact on click through rate.
For those of you who are unfamiliar with Adwords Sitelinks, they aren't new - they have been around since late 2009. They are links to particular pages of your site that you can add to an Adwords campaign so that they show up directly underneath your Ad - kind of like site links in organic listings. The big difference is that you get to decide what the links are and where the links are pointed to on your website. According to Google Adwords Help on the topic "The sitelinks ad extension lets you show links to pages from your website, in addition to the main landing page, beneath the text of your ads."
It is a pretty cool feature and Google will show up to six site links attached to any particular Ad, all at no extra cost (actual number of site links displayed will depend on the browser and form factor (desktop/tablet/mobile)
By most studies, Adwords site links can increase CTR by 30% with the added benefit of having your ad take up more real estate in the search listings (making your competitors ads or organic results farther