Google's orkut social networking site is now integrated with Google Talk. When you log into orkut, you'll see presence information for each of your orkut friends, and can launch an IM window by clicking on them. You'll also receive notifications when people leave scraps (comments) on your orkut page. And if you choose the "Automatically include all orkut friends" option (the default), your Google Talk friends will be kept in sync with your orkut friends.
Here's my (admittedly boring) orkut page.