For the past few days with the help of Greg Beaver (CelloG), I have been implementing user notes in the pear user documentation. This is now live and running using text-captcha-numeral and an administration backend where any developer can approve comments.

[...] Anyways, this is currently working, you have to go on a package's documentation link and then click on end-user documentation. You will then notice at the bottom a link that says "Add a note/comment".

He's also looking at adding some Javascript functionality to make it a bit more "pretty" (some jQuery features like popups/fading/etc). You can see an example of it already on the MDB2 documentation page.