I have been getting emails, Twitter messages and seeing threads that more and more people are seeing this newish kind of Sitelink. It isn't brand new, it has been around for some time now, but it is 100% showing up more often in the Google results. You can probably trigger it yourself for many types of queries, but I know this one is working for me. Search for [google sitelinks forums] and you will notice these newish Sitelinks formats coming up, not once, but twice. Here are screen captures:
If you scroll down, you also see:
As you can see, they offer more links from the same site with added data (such as date of post and number of posts, if a forum thread). This is a mix bread of Sitelinks and content attributes in the search results.
So this format is coming up more and more often, as opposed to standard Sitelinks. I find these types of Sitelinks to be deeper, so I am calling them "Deep Sitelinks."
Forum discussion at WebmasterWorld.