those allow you to send a link of that particular post or thread to one of the sites that they link to.
the first one would submit the story to digg, the second to delicious, third to technorati and then the last to furl. these are all social bookmarking sites. people submit stories or links, they get posted, bookmared and/or voted on/discussed.
delicious and digg are pretty rad sites. delicious allows you to make groups and you and your friends can dump a bunch of links to them and all keep up on common news.
And what happened to the functionality of the little "new posts" button next to the thread titles? I click on it to see the newest posts, but it just takes me to the top of the page & I have to click on "View First Unread." Weird! But I enjoy how we get new little features from time to time.