Rated 4 out of 5 stars
Seems to work reasonably well, except for the fact that it doesn't Google Reader tabs always stay unread. That's because the page itself never scrolls, only the inner frame, and informational tab denotes a page having been read by if you have scrolled in the main page. I would rather a page be considered read simply by viewing it.This review is for a previous version of the add-on (0.2.2008062001).
How to make tab "read" only by viewing it
There is an option to change the behavior. See the "Unread status" panel in the configuration dialog of Informational Tab.