If you have commented on my blog you have likely noticed this blue Gravatar image appearing next to your post. This is the default image that appears if you have no avatar, and you really should get one. I've been on a total avatar kick lately. I had my own custom avatars made. I think that this is part of keeping the Internet personal and "connected". I love to fill in my OS X Address Book with pictures for people so that when they call or I get email from them I get to see them.
A gravatar is a globally used avatar. It's a service that takes your email address and creates a key to map it back to your gravatar. Automattic now owns Gravatar and is embedding it into WordPress. Now there is a plugin for the OS X Address Book that allows you to pull Gravatars into the Address Book.
So, why wait? Go to Gravatar and personalize yourself. It's cool!