Komnt let's you comment the web!
Simply hold down Ctrl/Cmd and select any text on the web. Then Komnt will allow you to add a comment to your selection and share it with your friends.
Keep in mind Komnt needs to be installed on the recipients browser in order for them to display/edit your comments.
For now, Komnt uses the address bar to persist your comments. This means there is a limit to how much you can comment. In the future I'm definitely planning on making it persist the comments on an external server, so stay tuned :-)
Thanks to FlatUI for their beautiful buttons and color palette: http://designmodo.github.io/Flat-UI