To activate this feature, go to your Settings page and click on Edit Connections at the lower left side.

This enables the "Like" button to appear at the top of threads and various other spots on the forum. I'm not sure how many of us are active on Facebook, but I thought it was a neat feature to enable. This is due to the newest version of vBulletin I loaded this evening. I'm still checking out some of the other features that have been added since the last version.