I don't use any bookmarking tools with any regularity other than Instapaper, and I don't need an extension that does anything beyond simply sending articles into the service. This extension aims to make that as simple and streamlined as possible.
The extension has two features:
1) Clicking on the instapaper icon in the address bar will submit the current tab's URL/Title to Instapaper for later reading.
ctrl-p on any page has the same effect.
The first time you attempt to submit a URL, a popdown will appear, asking for your Instapaper username and password. As soon as you enter a working pair, the URL will be submitted, and you can move on with your life.
None of these behaviors is in any way configurable.