The theme is AWESOME. In Thunderbird, in particular, it seems to finally allow TB to express the whole set of its possibilities: which, one way or another, the standard theme has never allowed to.
Just a suggestion, though: wouldn't it be possible, in future releases, to add the possibility of changing at least SOME of the parameters of the theme? For example: the dominant color. That sky blue is cool... but I'd prefer something else ^_^