Because Twitter has such tight restrictions on what you can squeeze into a single tweet (140 characters), that it’s imperative to shorten a URL before you tweet it.
Shorten URL does exactly that. It will automatically shorten the URL of the selected NetNewsWire item and send it to the clipboard for later use.
Shorten URL uses the actual is.gd API. Of course, if you wanted to use a different shortening service you could just change the URL and parameter syntax as appropriate.
Use Shorten URL with any headline selected or on a web view tab, and you’ll have your shortened URL right on the clipboard.
Installation: Download it, decompress it, and place it in ~/Library/Application Support/NetNewsWire/Scripts. It will automatically show up in NetNewsWire’s scripts menu.