I noticed that Mozilla Update now has a bunch of themes for Thunderbird. So I downloaded and installed them all.
So far I like the Noia/Cute theme best of all. It's a trendy shades of grey with aqua highlights. The Thunderbird icon spins when Thunderbird checks the mail servers. And the unread mail icon is a paw print!
Look at all those unread
There were a few problems with the theme though. Firstly, the download link at Mozilla Update doesn't work. That's simple to get around as the jar file is also available at the theme's home page. I don't know why this can't just be corrected though as it seems almost every other question in the feedback is about the download link not working.
The second problem is after installing the theme, the preview pane goes blank. Again, this is easy to work around by temporarily changing the View Layout and then changing it back. I posted a note about that in the feedback.
The third problem, the only one that wasn't so easy to correct, is the junk mail status icon is blank. I noticed that it is a problem with some of the other themes too so I'm wondering if those themes were all assuming a default junk mail icon that is no longer there in Thunderbird 0.7.3. Anyway, it took a bit of trial and error but I fixed the problem by adding an icon to the theme. It's just a zip archive with lots of image files so that wasn't hard to figure out.