The US market test is currently running on a small percentage of searches on Bing and will be rolling out to Yahoo Search, as well. It will be seen on the first three ads appearing at the top of the page. The goal, says Microsoft, is to improve click-through rates.
If the first sentence of the descriptive copy ends with a period, a question mark, or an exclamation point, it will be added to the headline with a hyphen as a separator. If that first descriptive line is too long, the display URL will be added instead, excluding any www or URL extensions, and with a “|” separator. When those elements are “promoted” to the first line, they are omitted later in the ad.