The meta description isn't going to help with getting a page's rankings but in the social world it's often times the text that is automatically pulled into a social site. The best example is Facebook. When you add a link to your Facebook wall, it automatically pulls the title tag, meta description and let's you choose an image. Think of the meta description as a way to entice users to click on your link whether the user is searching on Google or checking out a page you shared on Facebook