As of the writing of this post, this service has been removed from Feedburner, but still works. Who knows if Google's planning on getting rid of it in the future? But for now, here's how to use it yourself...
To activate this for your own blog:
First, log in to your Feedburner account and choose a feed.
Your address will include an "id" field that's a string of letters and numbers... That's the ID of your feed.
Take that ID, and append it to the end of the following link:
As long as Google hasn't disabled this completely by the time you're reading this, that'll take you to the Socialize config. Just set it up, click "Save" and away you go.