One tiny problem... Rated 4 out of 5 stars
Great add-on! Working as advertised. Would possibly like some more customization as others have mentioned.
Also, it is not registering with Growl using the Thunderbird icon. Instead I just get some generic "globe-networking" icon. I de-registered TB from Growl, uninstalled the add-on, hacked it, then reinstalled it, re-registered with Growl, but it's still not using the correct icon. It's really bugging me! Otherwise really good!
Growl - 2.1.1
Thunderbird - 24.0.1
OSX - 10.8
Update: Started seeing the "Drafts" issue that @Anthirian reported below. I also support being able to ignore certain folders, as this was quite annoying when composing a lengthy email. System updated to TB 24.1.0, and OSX 10.9.