Rated 4 out of 5 stars

I like this add-on, but I think the arrows are backwards. Wouldn't it make sense for 1 receipient to have 1 arrow, and multiple recipients have multiple arrows? Confusing.

Also in the actual column, why does it show the arrows twice? Two sets of double arrows or two sets of single arrows.

This review is for a previous version of the add-on (0.1). 

Thanks for the review. I'm glad you like the plugin. First, the double errors issue is a bug and has been fixed already. Most recent version is 0.4, which has unfortunately not yet been reviewed by Mozilla. Besides the bugfix it adds a number of new languages. You can download the most recent version here: https://addons.mozilla.org/en-US/thunderbird/addon/personal-level-indicators/versions/

Second, I understand your concern regarding the semantics of arrows, however, I'd like to keep it compatible with Google Mail's behavior: http://mail.google.com/support/bin/answer.py?answer=8156