Stories that begin to experience a heightened amount of user interest in the form of off-site sharing, user discussion, and of course Diggs, will be presented up at the very top of Digg's home page, as well as being spouted in a special RSS and Twitter news feed. Once at the top of the page, those stories have 10 minutes to get voted onto the front page as a normally dugg story, otherwise they're buried into Digg's dead pool. All the while a giant counter ticks down how much time the story has left.
Along with the countdown timer, Digg is also putting forward some of its outgoing traffic numbers. Users can see how many clicks a trending story has gotten from the front page. Normally, the only other traffic numbers you see on a Digg story is when you're on the source site itself, though users must have the DiggBar enabled.
This new system is a stark difference from the somewhat nebulous promotion algorithm that exists for regular stories. Under the current system, stories have to earn their way onto the front page which involves standing out among an ever-growing pool of other upcoming stories. The company made this process a little more custom-tailored with the introduction of its recommendation engine, but it still requires that users actively visit that part of the site to see what's new. The new trending idea puts some of those stories up for everyone--and right on the front page.
In a company blog post about the new process, Digg's senior software engineer Kurt Wilms called it an "experiment," and said that it could change based on user feedback. Some Digg users have already voiced their opinions in the posting's comment section, citing that "bury brigades" (groups of highly opinionated users) could keep some stories from ever making it past their 10-minute window. The end result being that a story that could have legitimately made the front page on its own gets shut down before ever having a chance under the normal algorithm.
As with other new features, Digg seems to be rolling out Trends slowly, and to a small group of users. I'd expect it to show up for everyone in the next day or two.