Gravatars not appearing after 2.5 to 2.6.2 upgrade

I had previously used a plug-in for gravatars and identicons in 2.5 (but disabled and deleted it because of the load). Upgrading to 2.6.2, I see that the option is in the admin panel. But when I turn it on, nothing happens. Is this something that is theme dependent (we use a customized Kubrick)? If so, are there instructions anywhere on how to get it working. I’d really like to hook into the admin controls for this, rather than have it be completely manual from hacking themes each time we change it.