Update (June 2011): Google has now enabled embedded sitelinks.
Update (May 2011): Google is now putting the URL after the headline if there is space.
Update (Feb 2011): Google wrote a post about it for more information.
I was doing a test search for a campaign I was setting up today and noticed that the description line 1 was showing up right after the headline on Google Adwords. Apparently they’ve been testing it around the world for a while and is now showing up intermittently here (see this article).
Update: It looks like your ads will do it if description line one is a complete sentence (i.e. ends in “.” or “?” or “!”).