In February 2012, we improved sitelinks by using text from other ads in your account or My Client Center to create sitelinks with additional detail. Today, we’re going one step further by enabling you to nominate specific text for your sitelink descriptions from within your AdWords account. This will allow you to control the descriptions that display when this sitelink format shows.Google AdWords Now Allows Specific Text For Sitelink Descriptions [adwords.blogspot.com]
The new sitelink format with additional detail is available only in enhanced campaigns.
Note that your ads won't always show sitelinks, and when they do, the format that appears could vary.