Only seeing default Gravatars displayed on individual posts

I’ve got a WordPress 2.5.1. installation (not upgrading to 2.6 until the new version of podPress comes out) and I’d like to use Gravatars. I installed the Gravatar plugin from gravatar.com last night, and it did add some code to my comments template. Problem is, only default Gravatars are being displayed. I know that I and some of my regular commentators have working Gravatars, because I can see them in the Comments section of my WordPress control panel. You can see an entry page from my blog here. Commentators named “Shawno” (that’s me) and “Andy Melton” have known-to-be working Gravatars, but as you can see, only defaults are being displayed. Any assistance would be appreciated.