We just launched the Repost button 
If you don't see the Repost button below posts, be sure to refresh the page in your browser.
When you press the Repost button, the original post will be locked in the Omnibar. You can add your own comments & content before you submit.
Reposts will always display the original poster (Source), as well as the previous Reposter in the chain (Via), in order to maintain attribution.
If you delete your own post and it's been Reposted, all Reposts will be deleted too.
If you click the number next to a Repost icon, you can see a list of everybody who's Reposted. A number will only be shown if there's been a Repost.
In Settings, you can choose whether or not you want to allow others to Repost you. We've defaulted this to YES.
You also have a new Reposting filter in the Notification Center!
And if I haven't said the word enough times here....
REPOST! (and enjoy)
