THe mouseover to display the eye, pencil, and plus symbols is not obvious. THese icons should just be displayed at all times IMO.

It would be cool to write an annotation @ someone and then that person gets a notification through email or the plugin itself.

A nice feature would be mousing over the highlighted areas and having a popup show the annotation and the reply stream.

Theres some funky stuff going on above the header as the page scrolls. Header needs to be ~5px higher??