That is actually custom code that we added to Lithosphere to make it easier for you to quickly scan threads. I would love to see it as a core feature (maybe add that as an idea here: http://lithosphere.lithium.com/t5/Ideas/idb-p/Lithium_Ideas). For now, if you are interested in implementing this on your own site you can either contact Professional Services or if you have developers I can share a bit of how we are doing it.
If you have a developer on your team, here's a previous post I made with some of the details Kaela referenced:
Very nice, Adam! Didn't realize you had written that up.
k
