New interface feature from Google - I'll dub it "Google Arrows."

I was shocked to see this new feature in my Google SERPs today. It doesn't require personalization to be turned on, and it appears (for me at least) across an incredible variety of search results. It appears to correspond somewhat with the multiple page listings that often follow highly trafficked or searched-for sites and provides AJAX-like functionality, dropping down the other listings and allowing a searcher to get more information about the website, although it's hard for me to identify at this point where the text is coming from (appears to be a bit fuzzy and fluctuating at this point).

A visual example:

If you follow the link for the search phrase (search engine marketing), you'll see a great number of the listings have this arrow (unless it's just my datacenter). The odd thing is, I ran more than a few searches this morning and didn't spot it until just now.

If this listing format sticks, I think search marketers are going to need to concentrate very hard on how it affects click-through-rates. Optimizing this new, longer "snippet" could become a massively important part of a search marketing campaign.

Is anyone else seeing this yet? What's your opinion about the source of the text and short/long term effects of the new "Google Arrow"?