Surprisingly, Thunderbird 0.7 RC is still using the Qute theme (i.e. you can still see the name Arvid Axelsson in the theme manager). Maybe that's because Kevin Gerich and Stephen Horlander are still busy improving the Winstripe for Firefox 0.9 RC.
Like Firefox 0.9 RC, there are some similar changes on it.
P.S. When the Winstripe for Thunderbird is out, I might post a screenshot here! ^__^