The final sharing feature we're putting into place right now is Instapaper. A story can be individually saved to your Instapaper account from the same Share menu that offers Email, Facebook, Google Reader, and Twitter sharing, but there is also an option on the Settings page that can post any item to Instapaper when it is starred.

Since Instapaper doesn't support OAuth you will need to provide your user name and password. The first time you post an item to Instapaper you will be prompted for your credentials so you don't need to set up the service in advance.