Rated 4 out of 5 stars
This add-on is very good space saver. Must-have in computers with small resolution (laptops) where every pixel has price of gold. And moreover, it looks damn nice too : ). Hopefully we see a Thunderbird version also in someday.
BTW latest version (20111112) seems to have back this issue that titlebar is little bit too high, couple of pixels empty space below close/maximise buttons (XP, FF8).